Serving soldiers, sailors and airmen and ex-servicemen across the UK are preparing to organise what they hope will become a mass protest march on Parliament and 10 Downing Street to register growing disquiet over underspending on defence and its impact on the military covenant.

The demonstration proposal has been seized on by the many thousands of active personnel and veterans who are members of unofficial websites such as the Army Rumour Service, the aircrew section of the Professional Pilots' forum, its RAF equivalent E-Goat, and Rum Ration, the Royal Navy and Royal Marines' site.

Despite a Queen's Regulations prohibition on uniformed servicemen and women taking part in "political" demonstrations, supporters of the protest say they would turn up in "civvies" and maintain a peaceful and dignified approach.

Organisers are also preparing to contact the Countryside Alliance for advice on the practicalities of co-ordinating a legal demonstration which could draw in sympathisers from all over Britain. The Alliance drew almost 500,000 to protest against anti-hunting legislation in 2004.

An approach is also to be made to Scotland's Save the Regiments' campaigners who organised a similar, if quieter, march through central London to register their opposition to the amalgamation of Scotland's six historic regiments two years ago.

Among the suggestions from supporters of a pro-military march is a proposal to walk en masse down Whitehall to No 10 and form up before staging an about-turn to face away from Downing St and the MoD as a gesture of disgust.

Another suggests forming up outside Buckingham Palace, a salute to the monarch, and then a march to Downing Street for a two-minute silence outside Prime Minister Gordon Brown's official residence.

One potential organiser wrote: "The precedent of the police marching over pay blew the argument of political neutrality' out of the water. The only way things will improve for the forces will be if significant public opposition is mobilised.

"This sort of thing would get tens or hundreds of thousands marching.There is an enormous amount of support amongst the public and plenty of serving and ex-serving supporters."

Another said: "The recent spate of stories about MoD mendacity and vindictive tight-fistedness are enough to make your blood boil. The same lies are recycled by mouthpiece ministers, yet the same outrages keep happening. The government commits troops to operations with all the forethought of a gambler with a blank chequebook.

"Parliamentary accountability is at an all-time low, with no annual Defence Vote and the same recycled lies, fiddled figures and promises of equipment some time in the future. The armed forces are in a terrible state and it only appears to be the pride and sacrifice of personnel that is cynically taken for granted by the government that keeps things creaking along."

A female relative of an RAF Hercules crewman lost in Iraq said: "It's about bloody time the government realised they can't take advantage of those institutions they think won't fight back. As a nurse, I've sat back and had it done and as someone who lost a loved one through penny-pinching in the armed forces, I want to help.

"The negative publicity of trying to ban a march and gag supporters of the armed forces would have a huge impact. It would look bad for a government which claims it can deliver democracy abroad, but can't practise it at home."

The MoD said service personnel were forbidden to take part in political demonstrations. Last year's Gay Pride march in London, attended by RASF personnel in uniform, did not count as "political", a spokesman added.