Stella Rimington, the former head of MI5, is to take the unprecedented step of going on the road to promote her controversial memoirs, due out next month.

Rimington, 66, the first female head of the secret service, has decided to speak about her life and discuss her book for the first time during a special public session at the Cheltenham Literary Festival on October 15.

News of her unexpected personal appearance comes only a few weeks after the work was finally approved by the Home Office. Permission for publication was given only after 'amendments and deletions' which were said to be necessary to prevent 'possible damage to national security'.

Many current and former members of the secret services are believed to see Rimington's memoirs as a betrayal. Those who worked with her under the restrictions imposed by the Official Secrets Act, such as the renegade MI5 officer David Shayler and the former MI6 employee, Richard Tomlinson, have since been legally prevented from writing about their experiences. Nevertheless, print revelations have become increasingly hard to stem since Peter Wright's book Spycatcher was published abroad in 1987.

Tickets for the event, to be staged in Cheltenham town hall, are disappearing at a record rate. Even though festival programmes were sent out only last week, almost half of the 1,000 available have already been sold.

'It is quite something,' festival director Sarah Smyth told The Observer this weekend. 'We have never had such interest in an event so early on.'

The cuts made to Rimington's book are believed to include sections discussing operations against the IRA, and MI5 actions during the miners' strike in 1984.

Those close to the author say there is 'no doubt' that she is planning further promotional engagements after the book's publication.