Dara's base at RAF St Athan is earmarked for 500 job cuts

But a planned union meeting with Defence Secretary John Reid was cancelled after Thursday's explosions in central London.

A group of 150 staff from the Defence Aviation Repair Agency (Dara) at RAF St Athan, near Barry had travelled for a lobby on keeping jobs at the base.

The Amicus union said a meeting would be rearranged in the future.

But a spokeswoman said anything more on Thursday would have been "inappropriate" given the events which unfolded in London.

Hundreds of posts are being lost because of a UK Government decision to move work on fighter aircraft from RAF St Athan to another base in Norfolk.

Wales desperately needs to retain these skilled jobs and the UK defence industry need them too Cath Speight, Amicus' regional secretary for Wales

The organisation's general secretary, Derek Simpson said before the protest: "The decision to run down a world class facility at Dara makes absolutely no economic, strategic or military sense.

"We believe the closure of Dara will threaten UK security and cost crucial jobs and a world-class facility which has no equal elsewhere in the UK or Europe.

"We hope to be able to persuade the secretary of state of our case."

The �80m facility, which was only officially opened in April and employs more than 1,400 people, has already cut 500 jobs after losing a number of repair contracts.

Mr Smith said RAF repair stands could be undermined if the works goes

In December, the UK government said it may sell Dara, which is a civilian arm of the Ministry of Defence (MoD).

Earlier this year, a spokesman for the MoD said that work on the Tornado F3 would remain at St Athan for the jet's lifespan, but that the situation after that was not yet known.

"Unless additional work can be found, it is unlikely we can maintain a viable business at St Athan beyond 2008/9," he said.

Unions have called for the plan to privatise the plant to be scrapped.

Cath Speight, Amicus' regional secretary for Wales, said before the workers left for London: "Wales desperately needs to retain these skilled jobs and the UK defence industry need them too.

"The taxpayer has already invested �80m in Dara and to upgrade the facilities at RAF Marham would cost millions more and will never match the facilities at Dara.