Who says that comedians can’t make a difference? When Tom Wrigglesworth stepped on to the 10.15 from Manchester to London last autumn, he was just a hangover sufferer with a yen for some peace and quiet. When he stepped off, he was a people’s hero, wanted by the police. And out of this bruising encounter with petty officialdom he’s crafted a beguiling hour of Fringe comedy.

Tom Wrigglesworth’s Open Return Letter to Richard Branson tells the story of how the lanky, frizzy-haired Yorkshireman was shaken from his solipsism by an officious train conductor who refused to let common sense or common decency intrude on his duties. Inspecting tickets, this jobsworth finds that Lena, the pensioner sitting opposite Wrigglesworth, has accidentally taken a train half an hour earlier than the one specified on her ticket.

His solution? To insist that she pay the £115 full fare. So Lena has to break into the money that she had kept to buy Christmas presents for her grandchildren. Wrigglesworth acts, going up and down the train to organise a whip-round; an act of dissent that the conductor doesn’t take lightly — he rings ahead to Euston to get him arrested for begging. In recounting all this, Wrigglesworth flits between an acute rubbishing of corporate overthink — the cup of tea he can’t take back to his seat for health and safety reasons, the Virgin Trains mantra of “we aim to exceed expectations” — with very human observations about his fellow passengers.

It’s a great story, warmly and wittily told, that comfortably exceeds expectations in all but a couple of ways. The digressions he makes from the train story reinforce his theme, and allow him to eke out his hour, but slow down the narrative. And, as this mostly delightful show comes to the end of its journey, his activism detours him into a slight preachiness. In championing a move away from a punitive pricing structure, whereby passengers can only buy a full-price ticket on the day of their journey, he has a real-world impact — Virgin subsequently changed its rules. You may emit a cheer and/or shed a grateful tear at this point in the show.

But isn’t the more important message here about being a human being, about not just blindly following rules, rather than about setting up new rules? So I’m not entirely convinced by Wrigglesworth’s consumer campaign — which you can read more about and support on www.lenaslaw.co.uk. Yet there is no doubt that he makes a strong case for himself as one of the most interesting young comedians in town.

Box office: 0131-556 6550, to Aug 31