Over three decades he had been an MP, government minister, privy councillor, peer and Labour grandee.

Yet, officials still determined Lord Mandelson couldn't be trusted to hold a security clearance that grants access to 'top secret' government material.

Shadow National Security Minister Alicia Kearns revealed the process for Developed Vetting is, unsurprisingly given the implications, arduous and intrusive, shining a light into every corner of an applicant's life and looks at the possible red flags that officials could not miss.

DEVELOPED VETTING

It does not matter how long a politician has been in government or what jobs they did previously, they still have to pass developed vetting for sensitive roles.

The United Kingdom Security Vetting, which is part of the Cabinet Office, is responsible for conducting in-depth vetting.

MI5 does not carry out national security vetting, but spies do have a key role in the process, submitting a report on possible risks, which can range from a one-line warning to pages of details about dodgy associations and potential blackmail concerns.

Based on that, report officials within the Cabinet Office carry out in-depth interviews, scrutinising the most personal and sometimes embarrassing aspects of an applicant's life.

Developed vetting is the highest level used by the Foreign Office and entails deeper scrutiny than a routine security check.

Applicants must undergo a rigorous process that includes a detailed questionnaire, character references from three close contacts, a thorough check of an individual's personal financial history and an in-depth interview with a security vetting officer.

Shadow National Security Minister Alicia Kearns recalls of her own vetting: 'It can be a brutal process. They ask you about everything – your sex life, your friends, past relationships, have you ever had an affair, have you ever used drugs, could you be a blackmail risk?

'They ask about social media, what countries you have been in, where did you stay, who were you with, have you ever accessed porn?

'It is an exhaustive grilling process. They literally ask you about every single aspect of your life.

'It is highly intrusive and deeply personal. It is a red line if you lie about anything.

'I remember at one stage being told I had lied because I said I did not use social media regularly.

'They pointed out that I sent a tweet roughly every week.

'I had to tell an older man that in comparative social media terms, that was nothing.'

Ms Kearns believes that there are multiple reasons why Lord Mandelson would have failed vetting.

EPSTEIN

At the time of the peer's appointment last February, there was a wealth of evidence in the public domain about Mandelson's close friendship with convicted paedophile Jeffrey Epstein.

A two-page Cabinet Office propriety and ethics report compiled for Sir Keir before he gave Lord Mandelson the top job, revealed the peer had stayed at Epstein's townhouse in 2009 while the financier was in prison.

At the time, Mandelson was acting as the de-facto deputy prime minister to Gordon Brown, having been bestowed various titles including Business Secretary and Lord President of the Council with the honorary title of First Secretary of State.

A 'summary of reputational risks' from publicly available information would likely have flagged an internal JP Morgan report from 2019 revealing Epstein 'appears to maintain a particularly close relationship' with Mandelson.

There had been numerous reports of Mandelson attending intimate gatherings at his Manhattan townhouse from 2002 onwards, including photographs that emerged of the pair celebrating a birthday at Epstein's Paris apartment in 2007, by which time he had been arrested, charged and bailed over soliciting prostitution from a minor.

It was clear at the time of his appointment that the pair had continued their friendship after Epstein was released from jail on a child sex-trafficking offence in 2009.

Files published last month show that the Prime Minister was warned before Mandelson's appointment that he had a 'particularly close' relationship with Epstein.

The dossier warned Sir Keir his pick for the job carried a 'general reputational risk'.

It is likely, therefore, that Lord Mandelson would have been asked about Epstein in his developed vetting interview.

Ms Kearns said: 'We do not know what he disclosed, whether he lied about his relationship with Epstein, which would be in itself a reason for failing vetting.

'But if the security services had sufficient concern about him staying with a convicted paedophile when he was effectively deputy prime minister, that could be a good reason for not granting developed vetting.'

Giles Dilnot, a former Home Secretary special adviser said: 'Given vetting isn't about uncovering wrongdoing but a severe assessment of risk – whether someone is likely, or possible to be exploited for secrets, and given the level our US ambo (sic) can see and Mandelson's known relationship with Epstein, I can't see he stood a chance of passing.'

LINKS TO CHINA

Downing Street was forced to deny reports six months ago that the Labour peer failed vetting because of concerns over his business links to China.

The Independent reported in September that vetting had not been approved due to China links and worries that his past friendship with the disgraced financier Epstein 'would compromise him'.

When asked if Sir Keir had pushed through Lord Mandelson's appointment despite not clearing vetting, a spokesman dismissed the question saying: 'Vetting done by FCDO in normal way.'

Lord Mandelson has long had a reputation for staunchly defending China despite national security concerns.

The peer co-founded Global Counsel in 2010, whose clients went on to include Chinese firms such as Shein, the fast-fashion firm, and TikTok, the social media giant.

Representatives from Global Counsel lobbied ministers on behalf of TikTok in the UK between July and September 2024, according to the lobbying register.

Officials described Lord Mandelson's role at Global Counsel as a similar 'reputational risk' in security documents published in February, and explicitly highlighted the firm's links to China.

Security advice passed to the Prime Minister stated that the peer would have to step back from the firm if appointed ambassador to the US, and Lord Mandelson went on to do so.

The security dossier also flagged as a reputation risk Lord Mandelson's broader stance as 'an advocate for closer UK-China relations'.

It pointed to comments he made in 2018 in which he said it was 'absurd to imagine putting a country of such weight in the naughty corner' and that Donald Trump, the US President, was a 'bully' for pressuring the country.

The document also cited a speech that Lord Mandelson made at the University of Hong Kong in which he underplayed mainland China's increasing grip over Hong Kong and called for closer UK ties to the region.

At the time, Lord Mandelson was making frequent trips to China and met with senior officials.

Ms Kearns said: 'His links to China may have been a reason why he failed vetting.

'His relationship with China was certainly known about at the time.'

Luke de Pulford, co-founder of the Inter-Parliamentary Alliance on China wrote on X: 'Strong rumour that Mandelson failed vetting because of his China links.

'Frankly it would have been astonishing if he'd have cleared it. Public domain stuff damning enough. No secret info needed.'

RUSSIA

Security officials also raised concerns about Lord Mandelson's links to Russia ahead of his ambassadorial appointment last year.

The Cabinet Office's due diligence report flagged his former role as a non-executive director at Sistema, which is a shareholder of the defence company RTI.

The report pointed out that RTI produced technology 'for Russia's land-based missile early-warning system', and described Sistema's chairman as a 'Putin ally'.

This connection was not listed in the reputational risks section of the security advice about the proposed appointment, but was included in a section of the report that listed previous media reporting about him.

This stated that he remained on Sistema's board until June 2017 'long after Putin's annexation of Crimea in 2014'.

The report did not mention Lord Mandelson's widely reported links to the Russian oligarch Oleg Deripaska, but he is likely to have been asked about this at the interview stage.

Lord Mandelson's friendship with the Russian billionaire, who at one time was Russia's richest man, has been known since at least 2008 – when the former Labour MP was EU trade commissioner.

A Sunday Times investigation at the time raised potential conflict of interest concerns, after it revealed that Lord Mandelson signed off tariff changes that benefited Deripaska's company after the pair socialised together.

Emails published subsequently in the Epstein files suggest Lord Mandelson tried to secure a Russian visa for Epstein using Deripaska's help.

Lord Mandelson told the convicted sex offender in 2010 that he would reach out to 'OD' to help, although the US billionaire later cancelled his plans to travel to Russia.

FINANCES

Lord Mandelson has repeatedly faced questions about his finances.

In 1998 he was sacked as trade and industry secretary, after it emerged that he had taken a secret interest-free £373,000 loan from Geoffrey Robinson, then paymaster general, to buy a flat in Notting Hill in 1996.

Following his return to politics, Mandelson purchased a £2.4million peach stucco villa on one of the most exclusive streets in London overlooking Regent's Park in 2006.

The price was around 16 times his then-income as a European Commissioner.

Sources close to the then Mr Mandelson suggested at the time that he used a bequest from his late mother and sold his shares in an advertising agency.

But probate files showed he received only £452,000 from his mother's estate.

He took out a mortgage reportedly for £750,000, but let slip in 2009 that he had managed to pay it off in just a year.

Later, Mandelson also found the money to buy a £7.6m house in the same neighbourhood in 2011, which police raided earlier this year as part of their investigation.

In 2020, the Sunday Telegraph alleged that Mandelson was paid by a company whose job is to provide 'inside information' for its clients, principally hedge funds.

Officials subject to developed vetting must disclose information about mortgages, as well as 'all loans and personal contract purchase (PCP) agreements (including their purpose), credit cards (including store cards) and overdrafts'.

Police are now investigating the peer over allegations of misconduct in public office following claims that he passed sensitive information to Epstein during his time as business secretary.

Today, the Chief Secretary to the Prime Minister Darren Jones told the BBC's Today programme that he did not know the reason why the peer failed vetting, but said: 'I've not seen the documents or the detailed information, as I say, this is deeply personal information about financial, personal backgrounds and particular views and relationships.

'It's normal for that information to be kept only by the security officials who conduct this work, because it is so invasive into people's personal lives.'