Civil servants are faking coming into the office with some working from home for years, it has been claimed.
Some mandarins have been accused of driving to car parks near their offices so they can register their attendance on the internal Wi-Fi before heading home again.
The practice has reportedly become so commonplace at HM Revenue and Customs it has become known as a 'drive-by log-in'.
The tax collection department has faced major criticism in recent years over the standard of its customer service.
A report last year found that it cut off calls without explanation from 44,000 customers who had been waiting 70 minutes to have a query answered.
Office statistics show that HMRC head office occupancy has been rising since Labour took power.
But whistleblowers said that some offices were 'like the Mary Celeste' on Fridays with staff flouting rules saying they should be in the office three days a week.
Some mandarins have been accused of driving to car parks near their offices so they can register their attendance on the internal Wi-Fi before heading home again
One HMRC official told the Telegraph: 'You can go years at a time without seeing certain colleagues.'
The paper found that some 4,000 of the department's 70,500 staff, some 5.6 per cent, had been away from the office for six months or more, although the figures included holidays and sick leave.
At Land Registry some 200 staff had been away for half a year or more.
Reform's Danny Kruger said: 'The Government should order an immediate investigation into the productivity and workplace culture at HMRC and the Land Registry.
'This is part of a general problem, especially in departments like these that don't answer directly to ministers. The Civil Service has grown by 20pc in the last 10 years to over half a million people – many of whom are clearly not delivering for the taxpayer.'
A government spokesman said: 'We are clear that a minimum of 60pc office attendance remains the best option for our staff and the public.
'This data represents a fraction of staff and includes people on long-term sickness, maternity leave and those who work in other locations or deliver services on the front line as part of their work.
'Attendance is managed within teams, and managers have our full support to initiate disciplinary proceedings if necessary.'