Five hundred jobs are being cut at the jet repair centre

Staff working for the Defence Aviation Repair Agency (Dara), including many from RAF St Athan in south Wales, will rally in central London on Wednesday.

Union leaders said the planned cuts would harm the support given to servicemen and women in the frontline.

Up to 500 jobs are to go at St Athan when the �130m fast jet operation switches to an RAF base in Norfolk.

Armed Forces Minister Adam Ingram has said the UK government's investment in the project will be recovered by the time fast jet work finishes in 2007 - even thought the Ministry of Defence (MoD) is pulling out earlier than planned.

But union leaders have warned that thousands of jobs could be lost and millions of pounds of taxpayers' money "squandered" by UK government policies.

More than 500 workers from across the UK are expected to take part in the protest.

The protesters, accompanied by Wales rugby international Dwayne Peel, will demonstrate outside the MoD before attending a rally and then lobbying MPs at Westminster.

'Serious threat'

Mark Serwotka, general secretary of the Public and Commercial Services union, said members were travelling to London to say "enough is enough".

Mr Serwotka said the cuts would have a "devastating impact" on the communities and local economies affected.

He added: "In the meantime, we also have a massive programme of privatisation of key areas of defence with private defence companies lining up, hoping to swallow up massive contracts worth billions which are often only renewable after 25 years.

"Members will be raising these issues with their local MPs to enlist their support for our ongoing campaign to save Britain's defence from this most serious threat."

Over the next few weeks, union officials will also meet defence workers across the UK to prepare for an industrial action ballot in protest at the decision to close St Athan.

'World class'

A joint union statement said: "We believe that these plans will, at the very least, result in greater expenditure and heavier reliance on monopoly private suppliers.

"At worst, it represents an attack on the ability of our armed services to function and may jeopardise frontline armed services and service personnel safety."

The decision to close the site has been criticised by many of Labour's own MPs.