Fancy-dress runners in training are like baby pigeons: you know they exist but you never see them.  Then a big race such as the Flora London Marathon arrives and you find yourself lining up at the start next to Batman, a hotdog, Minnie Mouse and a giant banana. 

A pair of shorts and a vest might be as fancy as you usually dress, but if you want to push the boat out in a race, fancy dress is a great way to attract attention and boost charity donations.  How, though, do you choose an outfit that allows you to enjoy the event as much as the spectators cheering you on? 

When Tom Day started running for Leukaemia Research after his father was diagnosed with the disease, he decided to become part of the charity's Banana Army at last year's London Marathon.  Running a previous race dressed as a whisky bottle taught him the value of a costume that is up to the task. 

"The shoulder strap broke and I ended up running with it balanced on my head," he says. 

He also recommends being able to see out of your costume. 

"Not only will it stop you tripping, but when you're in fancy dress half the joy is seeing what's going on around you." 

Having been diagnosed with leukaemia as a child, Nick Eagling decided he would raise money for Children with Leukaemia by dressing up as Mr Bump.  He trained with a weighted rucksack before a dress rehearsal at the Liverpool Half-Marathon. 

"This made me realise where my costume rubbed and that it had a lot of up-and-down impact," he says. 

A few minor adjustments made for a more comfortable run at the main event. 

"I added neck and shoulder padding made out of cushions," he says. 

Even if you skip the dress rehearsal, you're going to have fun running in costume. 

Mat Wilson, who works for the charity Cardiac Risk in the Young, has run the London Marathon three times dressed in one of the charity's heart outfits. 

"The costumes were designed by a non-runner," he says, "so they are a bit restrictive around the knee, but the wonderful crowd support more than makes up for moving at a shuffle." 

Eating and drinking when you're moving slowly shouldn't be a problem - as long as you can reach your mouth.  Eagling, for example, opted for a hydration pack under his costume. 

"Despite the heat, the race was one of the best experiences of my life," he says. 

Don't imagine that fancy-dress runners aren't competitive.  If you've seen a tree, wristwatch or running shoe weaving along the Mall, the chances are that the award-winning runner Lloyd Moreton was inside it.  He won a prize for dressing up as a music-pumping stereo speaker at the 2005 London Marathon, and often finds his way on to television. 

"It's worth being prepared for an interview", he says. 

"When I was a tree I joked, 'I'm bushed, and am I on the right root?'  The interviewer loved it." 

Dress code

Build  your costume around a backpack-style harness for comfort.  Use material that won't dissolve or grow heavy with rain or sweat.

If your costume is heavier than your running kit, train by running with a weighted rucksack. 

Be prepared for a slow time from the added bulk, but also because you may not be able to run full-length strides. 

You'll raise more money and perhaps attract television attention if your costume is original, crowd-pleasing and topical. 

If you have restricted arm movement or access to your mouth, carry water, energy gels or bars and medication inside your outfit. 

Display your name and that of your charity in a prominent place on your costume. 

Practise running in your costume in a shorter race to assess where it might rub.  You can then make adjustments, such as adding padding or lubrication. 

Have a few words prepared in case you are stopped and interviewed.