The RMT faced a growing backlash over its plans for eight Tube strikes ahead of Christmas and into the New Year.

The Conservatives accused the “militant” union of inflicting the wave of industrial action on the capital for “totally spurious reasons”.

The row is over a voluntary four-day week for Tube drivers, many of who earn over £70,000 a year.

The RMT (National Union of Rail, Maritime and Transport Workers) claims that London Underground is launching a “wholesale attack on drivers' working conditions”.

But its stance has been hugely undermined by the Aslef train drivers’ union fully backing the reforms.

It stressed they will offer drivers the best working conditions on the whole rail network including less time at work and rostered hours being reduced from an average of 36 to 34 a week with no pay cut.

“Yet more pointless strikes called by the RMT for totally spurious reasons.”

The Orpington MP added: “With this useless Labour government and Mayor of London constantly caving into union demands it encourages them to do it again and again.

“And who loses out as usual? Fare paying Londoners of course.”

Laila Cunningham, Reform UK’s London mayoral candidate, stressed: “We all wish we earned more or worked fewer hours.

“But the rest of us don’t get to hold an entire city to ransom when we don’t get what we want.”

With the strikes threatening to hit shops, restaurants, pubs, theatres and many other businesses in their crucial run-up to Christmas and over the New Year, she slammed the ‘militant’ union, adding: “It's time to modernise the Tube.

“It's time to automate. And it's time to put Londoners first.”

Liberal Democrat London spokeman Luke Taylor, MP for Sutton and Cheam, emphasised: “Nobody doubts how hard Tube staff work to keep this city moving.

“But eight days of strikes running right through Christmas and into February will be a hammer blow for London’s small businesses, hospitality venues and hardworking commuters.”

The eight 24-hour strikes are on:

Transport for London (TfL) and the RMT have been engaged in talks for months to try to resolve the dispute.

But in a surprise move last Friday, the union announced the series of strikes.

TfL urged the RMT to put the latest proposals to its members to see if they would back them.

Nick Dent, Director of Customer Operations for London Underground, stressed: “Drivers can now choose to remain on a five-day week with a guarantee of remaining at the same depot.

“This will give our colleagues a real, meaningful choice on their working pattern without having to change where they work.”

TfL rejected RMT claims that the changes would increase driver fatigue and stressed they were voluntary.

But RMT General Secretary Eddie Dempsey said: “Our members are being asked to spend more time driving trains, accept longer and more unpredictable shifts and surrender agreements that have been negotiated and defended over many years.

“This is not about improving work-life balance. It is about squeezing more work out of fewer drivers while giving management greater flexibility at the expense of our members.”