Senior citizens, often considered harmless if inert, can acquire a capacity for rat-like cunning and far-flung exploits. This was the guidance yesterday of Saga magazine, which specialises in the age group, and it can call witnesses to prove its point.

Exhibit A is the actress Joanna Lumley, who has found a foolproof excuse for smoking in public.

Exhibits B and C are Terry and Monica Darlington, who at the ages of 69 and 68 sat down one night, thought: "We could bore ourselves to death, drink ourselves to death, or have a bit of an adventure."

Opting for the adventure, they embarked on a 1,600-mile odyssey by narrow boat to the Mediterranean with their dog, Jim.

Joanna Lumley's autobiography, No Room for Secrets, and Terry and Monica's story of their voyage, Narrow Dog to Carcassonne [sic] are on a seven-title shortlist announced for the Saga award for wit.

The magazine's editor, Emma Soames, who heads the judges, said laughter among the seniors was usually "all about sit-down, rather than stand-up comedy".

But she added: "Wit is a craft that improves with years of practice and, like a good wine, matures beautifully with age."

Joanna Lumley writes in her entry: "In the acting world, which used to be blue with smoke, most people have given up the weed. Only villains or 'characters' like Patsy in AbFab are allowed to smoke on film; actors often try to work it into their character's make-up, just to get a daily fix of nicotine.

"In real life, I smoke, but not very often. In coffee breaks on film sets, particularly with American actors present, I get out my packet of cigarettes with a guilty rush, saying, 'Oh Lord, I'm behind: my doctor said I have to smoke every two hours at least to get over this abdominal complication - what a bore'.

"Then I light up and puff away with a lugubrious expression.

"There is a clamour to find out my benevolent doctor's name, which of course I don't give because he doesn't exist."

Narrow Dog has been welcomed as a classic by one reviewer and is among Amazon's top 20 bestsellers.

However, Emma Soames said that, as a comedy about travel, it would have been overlooked by any other book prize shortlist.

Other shortlisted titles are: A Planet for the President, by Alistair Beaton; Lost Worlds by Michael Bywater; A Short History of Tractors in Ukrainian, by Marina Lewycka; Adrian Mole and the Weapons of Mass Destruction, by Sue Townsend; and Seeing Double, by Patrick Wilmot.

The winner will be announced at the Folkestone literary festival on September 19.