The first of two 24-hour strikes by London Underground drivers is under way after talks aimed at averting the action broke down.

Members of the Rail, Maritime and Transport (RMT) union walked out in a dispute over plans by Transport for London (TfL) to introduce a voluntary four-day working week.

The two sides met for last-ditch talks on Monday, but the RMT union said TfL had "failed to provide assurances" over concerns about longer working hours and driver fatigue.

TfL said it was "bitterly disappointing" but aimed to run at least half of Tube services.

A follow-up 24-hour strike is planned for Thursday.

The strikes officially began on Tuesday at 00:01 BST and very few services are to run before 06:30 or after 21:00.

The Circle and Piccadilly lines will shut down and parts of the Metropolitan line and Central line will be suspended.

Buses, London Overground, Elizabeth line, DLR and tram services will continue throughout but are expected to be much busier than usual.

Some residual disruption is expected on the mornings of 3 and 5 June.

TfL's proposal for a four-day working week would be voluntary and mean drivers would work slightly longer days, although they would work fewer hours per week and fewer hours overall.

Members of the trade union Aslef accepted the plans, but the RMT union voted to take industrial action, announcing several strike dates.

The first round of strikes in the dispute caused major disruption on the network in April.

Further strikes in May were called off after talks between the union and TfL.

However, following negotiations [with conciliation service Acas] on Monday, an RMT union representative said:

"Despite our best efforts in ACAS talks, TfL have failed to provide assurances on our members deeply held concerns around fatigue, reduced flexibility, shift lengths and the impact these proposals could have in a safety-critical role like tube driving.

"We remain available for meaningful talks, but strike action tomorrow will now go ahead."

A TfL spokesperson said: "It is bitterly disappointing that despite five hours of meetings with the RMT at ACAS and repeated assurances that the four-day working week proposals will remain voluntary, RMT has chosen to continue with its disruptive strike action.

"We will do all we can to provide as much service as possible during this action."

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