The triathlon season is well under way, and today is my first of the summer. However, in part because of a shoulder injury which has prevented me from swimming, I am taking part in a relay, with Olympic gold medal-winning canoeist Tim Brabants the one getting wet for the cause, before I get on the bike when he clambers out of the water.

It is the Bananaman Tri at Lake Dorney, its name drawn from the so-called Banana Army who do sport to raise money for Leukaemia Research. Tim lost his Mum to this horrible disease.

Triathlon is reckoned to be the fastest growing participation sport in Britain, and I recommend it to anyone who gets bored training in just one discipline.

When I first started doing triathlon, I had barely swum since school, apart from splashing around in a pool on holiday, and I had not owned a bike since I was 18. I actually went back to get proper swimming lessons, and as regulars on the blog will know, cycling has now overtaken running as my favourite fitness pastime.

They reckon the pressure on the body of a full Olympic triathlon (1500m swim, 40k bike, 10k run) is roughly akin to running a marathon. I’m not so sure about that, but one tip I will give to anyone doing a full triathlon for the first time — try to separate out the three disciplines in your mind. Don’t think of the race as a whole. Say to yourself you are going to swim a mile. Then you’ll get out of your wetsuit and onto a bike, which you will ride for 25 miles. Then you will change into running shoes and run 10k. When you’re swimming, think of swimming. When you’re cycling, concentrate on the bike. Try not to think ‘oh my God, all this, and then I have to run.’ And on the run, just grind it out.

We are a third of the way to raising the 50k in honour of Henry Hodge as part of our Big 5-0 celebrations of Leukaemia Research’s 50th anniversary, so thanks to everyone who has contributed. Anyone minded to join them go to justgiving.com/alastaircampbell.

Today’s exertions mean I won’t be with Fiona in Stoke Rochford as she receives the Fred and Anne Jarvis award for campaigning in education. As our children and I know very well, there is barely a day in any week when she is not fighting the fight for State schools, whether in general in the arguments she makes publicly or in taking up the cudgels for specific schools and specific children.

As my Mum always says whenever it is suggested one or both of us might stand for Parliament, Fiona would make a far better constituency MP than I would. She has more patience for a start. As it happens, I think it unlikely either of us will, though I think we have both learned in recent years there are lots of ways to try to make a difference. One thing is for sure, just as former NUT general secretary Fred Jarvis is still campaigning well past retirement age, so will Fiona. Whether I’ll still be cycling is another matter.

At least the sun has come out, which doesn’t half make a difference to triathletes getting out of the water and onto the bike. You should try it.