The armed forces are at risk of being hijacked by far-right extremists, a group of former generals has warned.

Today's Times reports on a letter outlining key concerns and signed by General Sir Mike Jackson and General Sir Richard Dannatt, the former heads of the Army, Lord Guthrie of Craigiebank, former Chief of the Defence Staff, and Major-General Patrick Cordingley, commander of the Desert Rats in the Gulf War.

The letter declares that far-right groups are "fundamentally at odds" with the values of the military, following the British National Party's use of images of Winston Churchill and pictures of soldiers in recent election campaigns. The party named its campaign for the European elections the "Battle for Britain" and used the Spitfire as its campaign logo.

The letter says: "We call on all those who seek to hijack the good name of Britain's military for their own advantage to cease and desist," they write. "The values of these extremists -- many of whom are essentially racist -- are fundamentally at odds with the values of the modern British military, such as tolerance and fairness."

General Jackson told the Times: "The BNP is claiming that it has a better relationship with the Armed Forces than other political parties. How dare they use the image of the Army, in particular, to promote their policies. These people are beyond the pale."

The generals' letter came as the BBC rejected a call from cabinet minister Peter Hain to remove BNP leader Nick Griffin from the panel on BBC1's Question Time this Thursday. The Welsh Secretary warned that the corporation could face legal action if it allowed Griffin's appearance to go ahead.

Hain argued that the BNP was an illegally constituted body after the party told a court that it would amend its whites-only membership rules to comply with discrimination legislation.

The BBC director general, Mark Thompson, responded: "According to the advice we have received, the British National Party is not prevented from continuing to operate on a day-to-day basis and its elected representatives continue to sit on councils and in the European Parliament. "It remains the BBC's obligation to scrutinise and hold to account all elected representatives and to do so with due impartiality."