Tube strikes were at the centre of a war of words between the current Conservative London Mayor and the Labour candidate hoping to win the job.

Boris Johnson took to Twitter posting: "Incredibly Sadiq Khan won't condemn this pointless strike. Massive support amongst Londoners for the night tube. He is stuck in the past."

That prompted the Tooting MP to reply: "During your Mayoralty the number of strikes has DOUBLED. I won’t take any lessons from you after your failure to stop strikes."

During Mr Livingstone's eight years as Mayor of London, there were 16 tube strikes, but there have been 35 in the same time period under Boris Johnson.

The next tube strike, which follows the dispute between union members and Transport for London over the introduction of the night tube, is to begin on January 27 with a 24-hour walkout.

Mr Khan, said: "It proves once and for all that the Tory strategy of refusing to negotiate or even meet with the unions makes strikes more likely not less.

"And it would be exactly the same under Zac Goldsmith - both he and Boris are more interested in scoring political points than stopping strikes.

"Londoners need both sides to talk and resolve their differences.

"As Mayor I will make this happen and stop strikes on the Underground."

In his 2008 manifesto Mr Johnson said: "I will look to reduce the disruption caused by strikes on the Tube by negotiating a no-strike deal, in good faith, with the Tube unions.

"In return for agreeing not to strike, the unions will get the security provided by having the pay negotiations conducted by an independent arbiter, whose final decision will be binding on both parties."

Mr Khan's campaign has blasted this claim, saying that Mr Johnson has not managed this deal and has refused to meet the trade union for talks.

The figures on the number of strikes since 2008 have come from a combination of Freedom of Information requests and answers at Mayor's question time.

Figures show there were six each year in 2008 and 2009, nine in 2010, three in 2011 and none in 2012 and 2013.

There were then eight in 2014 and three in 2015, giving a total of 35.

Disputes since 2011 have included Boxing Day payments and the transfer of customer assistants.

Mr Johnson said that the union turned down an "excellent" offer in favour of strike action.