London (AFP) - Beefeater guards at the Tower of London switched their traditional red uniforms for yellow vests on Friday as they went on strike with staff at other historic sites over pensions.

For the first time in 55 years, visitors to the mediaeval castle were met by a picket line.

Staff at the Historic Royal Palaces, including Hampton Court Palace and Kensington Palace, staged a walkout, donning the high-visibility yellow vests worn by demonstrators in France.

HRP has replaced their current pension system with a new one which includes increased employee contributions.

"Young employees will lose money with this new scheme," Theresa, an HRP employee approaching retirement, told AFP.

The change is all the tougher to swallow for these workers -- who say they are dedicated to their jobs and enhance the image of the British monarchy -- whose salaries are far from being "marvellous", said Theresa, who declined to give her surname.

"This is what kept us working for HRP for such a long period of time because that (old) scheme was such a good one," she said.

HRP said it had offered substantial compensation and transition arrangements to the 11 percent of staff who were affected.

But that was not enough to placate the strikers.

Determined to make themselves heard, they gathered outside the Tower of London, brandishing placards reading: "Defending our pensions".

"Although we fully respect the rights of trade union members to take industrial action, today's strike is disappointing," said HRP chief executive John Barnes.

"It will not change our decision to close the defined benefit scheme."

The palaces stayed open duing the strike.

Chris Baugh, assistant general secretary at the Public and Commercial Services Union, said: "We will continue until the employers will talk to us."

He said HRP's pension move was "unnecessary and unfair".

Beefeaters are the ceremonial guards tasked with looking after the crown jewels. They also welcome visitors to the tower.

Further industrial action is planned for later this month and in the new year.