London Underground staff in Wandsworth are to join three 24-hour strikes over pay and the introduction of the night tube as the battle between Boris Johnson and the unions intensifies.

Tube staff will strike for 24-hours from the evenings of January 26, February 15 and February 17.

Services on the Northern line throughout the borough will be affected.

January 11: Tube strikes have more than doubled under current London Mayor says Sadiq Khan

The strikes follow a dispute between the RMT (Rail, Maritime and Transport Worker's union), Aslef and Unite the Union as Transport for London (TfL) seeks to introduce round-the-clock services.

A statement from the RMT said it had written to London Underground ensure that "staff will not be forced to sign new contracts and that rosters will not be imposed".

Mick Cash, RMT general secretary, said: "The critical issues in this dispute that remain outstanding include no agreement over a new framework agreement, the proposed rosters do not comply with current agreements or assurances given regarding weekend working, the company is denying promotion and career prospects by recruiting externally, there is no guaranteed protection of earnings and no guarantee that vacancies on rosters will be filled."

RMT workers will strike from 9pm on each of the three days while Aslef workers will strike from 9.15pm on the same days.

On Monday, January 11, Sadiq Khan, Labour's Mayoral candidate and Tooting MP said that strikes had doubled under the leadership of Mr Johnson, when compared with strikes under Ken Livingstone, his Labour predecessor.

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 you [Mr Johnson] and him are more interested in scoring political points than stopping strikes.

"Every Londoner who wants fewer days lost to strikes needs a Labour Mayor.

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

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

Zac Goldsmith, the Conservative Mayoral candidate, and his team challenged Mr Khan to state the concessions he would make to "stop the strikes".

Mr Goldsmith has called for the Underground to be classified as an "important public service" which would make it harder for workers to strike.

He wrote to business secretary Sajid Javid to ask him to ensure that 40 per cent of the entire underground workforce voted in favour of strikes before they went ahead.

Stephen Hammond, MP said: "By saying he would negotiate directly, Sadiq Khan is sending his clearest signal yet to the unions that their demands are back on the table.

"With no more money available for the unions, fares would have to go up to pay for them. The question for Khan is which demands will he cave into and how much will fares have to go up as a result of his union bought transport policy?

"This is just another example of why Khan - who backed Jeremy Corbyn and would bring Labour's chaos and incompetence to City Hall - can not deliver a better transport system for Londoners."

Steve Griffiths, chief operating officer of London Underground said: "The unions' position is absurd and detached from the real world.

"Apparently, above-inflation pay rises, the creation of 700 more Tube jobs and the total protection of the work-life balance of existing staff are grounds for strikes.

"Our four-year pay offer is extremely fair and we have gone the extra mile to fully protect the work-life balance of all our staff.

"London needs a Night Tube service and we have made all of the running to implement it fairly. The only thing standing in the way is union intransigence."