IT is a Scottish military tradition that has remained unchanged for 140 years.

Each day at exactly 1pm, Edinburgh's timepiece, the One O'Clock Gun, booms out from the castle's western defences, evoking the days of the Empire and sending unwitting tourists running for cover.

But soon the famous gun could enter a new era under a sponsorship plan devised by the man who has fired it every weekday for the past 22 years.

Staff Sergeant Thomas McKay, better known as Tam the Gun, believes sponsorship of the weapon is the way forward - to secure its future and the future of an exhibition devoted to it.

The controversial idea, which could see the livery of a multinational company painted on the barrel of the gun, has already received backing from Major General Mark Strudwick, the governor of Edinburgh Castle and the GoC of the Army in Scotland.

Staff Sergeant McKay, 55, of the Territorial Army, said the gun was ''under-sold'' and merited a much higher profile.

''What we have here is one of the last cities on the planet that fires a time gun,'' he said.

''I feel that the One O'Clock Gun with its mind-boggling history, the countless tourists who have seen and heard it at first hand over the years, and what it means to the local population, is still under-sold. I'm sure there would be no shortage of sponsors but the commercialism would have to be handled with a certain dignity.''

He believes sponsorship would be essential to continue the One O'Clock Gun exhibition after its initial funding expires. The exhibition, funded with #30,000 from the lottery and #18,000 from Historic Scotland, tells the story of Edinburgh's time system set up in the 1840s and 50s by the Astronomer Royal for Scotland, Charles Piazzi Smyth.

Staff Sergeant McKay is the longest serving district gunner since the gun first fired in 1861 and is determined its role should be enhanced. ''I put my heart and soul into promoting it. I've never missed a day in 22 years, even Christmas and New Year's days. The exhibition is funded for eight years - then what? Perhaps by then a respectable form of sponsorship will be considered.''

Major General Strudwick said: ''Staff Sergeant McKay is a legend in his own time and everybody respects what he does. Sponsorship seems a reasonable idea and it may well be in the future that we'll seek some support.''

A spokeswoman for Historic Scotland said: ''The One O'Clock Gun is one of the highlights for the visitors to Edinburgh Castle. We will look at any ways that can improve that experience. Sponsorship is a possibility and we will be looking at that together with the Army.''