Shadow chancellor Ed Balls has revealed he is in training for next month's Virgin London Marathon - describing it as a "crazy" thing to do, given his day job.
The Labour MP, best known as something of a pugilist at the Commons Despatch Box, will be running 26.2 miles through the capital's streets for charity on April 22.
Mr Balls, already frantically busy holding Chancellor George Osborne to account and leading Labour's opposition to last week's Budget, has been secretly clocking up the training miles for six months.
He disclosed his secret running regime after somebody on Twitter said they had seen him in Regent's Park in London wearing "very tight, unedifying trousers".
Asked about the sighting during an appearance at the Guardian's Open Weekend, Mr Balls said he was, "completely madly", preparing for the marathon in four weeks' time. His training regime began in October and his longest run so far has been 18 miles.
"I'm finally at the peak of training. It's quite nerve-racking, the training's very hard. It's probably a crazy thing to do," he said - pointing out that senior frontbenchers rarely find the time to run a marathon on the side.
He said his goal was "just to finish", adding: "I'm not going to be that fast, to be quite honest."
Mr Balls is a keen footballer who regularly plays for the Labour team in their annual conference grudge match against journalists, but this will be his first marathon.
The Morley and Outwood MP is raising money for Whizz Kidz, which supports young disabled people's mobility, and Action for Stammering Children. Mr Balls has himself battled with a stammer all his life.
He will be among eight MPs who are to take part in this year's London Marathon - the joint highest participation by parliamentarians in the history of the event - but the only Labour name.