Staff at the National Gallery are going on strike for 10 days in their long-running dispute over privatisation.

Members of the Public and Commercial Services union will walk out from Tuesday, 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.

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

PCS general secretary Mark Serwotka said: "This privatisation plan is totally unnecessary and is damaging the well-earned reputation of the gallery and the sacking of our representative, Candy, is a disgraceful attack on our union.

"Our demonstration is not just about this sell-off and the victimisation of Candy, it is an opportunity to oppose the kind of Tory cuts being cited as a rationale to hive off staff to the private sector."

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 school-children 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."