MPs in starting blocks for London Marathon

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Media captionAlun Cairns hopes to beat his 2013 time of 3 hours 39 minutes

As political photo-opportunities go, it was slightly unusual. Ed Balls was wearing tights.

The shadow chancellor was jogging alongside eight other MPs who are taking part in this Sunday's Virgin Money London Marathon. Vale of Glamorgan Tory MP Alun Cairns is flying the flag for Wales in what will be his third marathon.

Mr Cairns is raising funds for local charities Marie Curie Cancer Care and Ty Hapus, a respite care centre for the families of Alzheimer's sufferers. You can sponsor him here. Charity aside, his politician's competitive instinct is never far from view and he hopes to beat his 2013 time of 3 hours 39 minutes, which made him the fastest Conservative MP.

So how's the training going? "It was ok until I foolishly played rugby in a charity match where the House of Commons and Lords played against the Welsh assembly. "I hurt my back just about a month ago, so I've had to run through that.

"Everyone says 'you shouldn't have played rugby, how old are you', those basic questions but ignorance is something we always continue to display."

More than 35,000 runners are expected to toe the start line, including Mo Farah, Plaid Cymru AM Bethan Jenkins - and me (three names you don't often see in the same sentence).

Alun Cairns said the crowds along the route "make you feel a million dollars" but he won't be taking his eye off his stopwatch. He has Labour's Shadow Foreign Secretary, Jim Murphy, in his sights. Mr Murphy ran 3 hours 31 minutes last year - the best by an MP on the day - but is aiming for 3 hours 19 minutes this year.

"I'll see if I can trip him up along the way," joked Mr Cairns. At least I think he was joking.

I'll update you on the politicians' times here next week. Unless they beat me, of course.