Staff at a leading gallery in Britain are to launch a 10-day strike in an escalation of a long-running dispute over privatisation.

Members of the Public and Commercial Services union at the National Gallery in London will walk out for 10 days from tomorrow, hitting the school half-term holiday.

There have been 24 days of strikes since February over plans to privatise services but this will be the longest period of action so far.

The dispute worsened when union rep Candy Udwin was suspended before the first strike and subsequently sacked.

Labour MP John McDonnell plans to raise her dismissal, and the privatisation, in the Commons.

A rally will be held in Trafalgar Square - close to the National Gallery - on May 30.

The National Gallery said it hoped to keep open as much of the gallery as possible, although it conceded that some families will be “disappointed” by the impact of this week’s strikes.

Thousands of schoolchildren have had visits to the gallery cancelled because of the industrial action.

A spokesman said: “The PCS opposes the introduction of a new roster for some visitor facing and security staff which would enable us to operate more flexibly. In conjunction with the new roster we also proposed not only to meet the London Living Wage, but to pay a basic salary in excess of it.

“As a result of the PCS position, we are now appointing an external partner to manage these services. Affected staff will transfer across - there will be no job cuts and terms and conditions will be protected.”

The gallery added it did not comment on individual disciplinary cases.