Among the 34,000 competitors lining up for this year’s London Marathon, there will be more than 2,000 teachers anxious to pull off their personal best on the big day.

But after months of pounding the streets during twilight hours, they will not only have a keen eye on their times - but also on the donations they will be able to make to their chosen charities.

The London Marathon now holds the Guinness World Record for being the largest annual fundraising event. Last year, runners raised pound;46.5 million, bringing the total amount since the race began in 1981 to pound;361.5 million.

Three of the teachers on the April 13 starting line will be Nick Brooker, Sophie Bryan and Emma Gilbert - colleagues from St Stephen’s Church of England Junior School in Twickenham, southwest London.

“We compare times, rather sadly, in the staffroom,” says Nick, 50, who claims it will be his first and only marathon. All three have signed up to www.justgiving.com - a website that has revolutionised how fundraisers collect donations.

Although the site, set up in 2001, charges a 5 per cent commission on gross donations, it is a no-fuss way of raising money from any sponsored event for the country’s most deserving causes. It saves you handling all those cheques and chasing up those who pledge money but never seem to be around when it needs to be handed in.

If donors click the Gift Aid box online, the charity claims back tax and for every pound;1 a basic-rate taxpayer gives, the charity receives pound;1.28. This is slightly less, of course, once you factor in Justgiving’s 5 per cent. But the website handles the whole process, saving everyone a lot of time.

Nick, a deputy head, is raising money for Oasis UK, which offers help to the world’s most disadvantaged communities, and for Macmillan nurses - in memory of his mother, Diana, who died of cancer last year. “My mum was sporty, and she would have been proud of her oldest boy,” says Nick. “That’s the motivation.”

Sophie, 33, is raising money for the Born Too Soon Fund at Kingston Hospital in Surrey, which supported her when her second daughter, Lucy, now 3, was born seven weeks early. And Emma, 34, hopes to raise pound;1,500 for the Anthony Nolan Trust, which finds bone marrow donors for those with leukaemia.

Helen Cameron, 37, another teacher at St Stephen’s, used Justgiving to raise pound;2,129 for Pancreatic Cancer UK last year when she took part in the Great North Run. She describes the website as brilliant. “Most charities are on there and it’s just so easy to use,” says Helen, who is training with her marathon-running colleagues in readiness for this year’s Great North Run in October. “You fill in all your details and then email all your friends for sponsorship.”

The not-so-sporty members of the staffroom, however, might be looking for a less physically demanding way of raising cash for charity.

Apart from making regular monthly donations by direct debit, there is now a range of charity credit cards that promise funds for named charities when you spend.

However, Martin Lewis of moneysavingexpert.com says you would be better off ditching them. “They are a hideous scam, selling us poor value credit cards on the pretence we’re doing some good. In reality, it’s just more profits for the banks.”

He points out that a charity receives between pound;5 and pound;25 when you first sign up for a card. After that, most cards donate a paltry 0.25 per cent of everything you spend - 25p per pound;100. In addition, these donations don’t qualify for Gift Aid.

It’s better than nothing, you might argue, but Martin recommends switching to a cashback credit card if you want to supercharge your giving. Opt for one of the highest paying cards and channel as much of your spending through it as you can. Give any cashback you claim from your spending to charity - and claim Gift Aid.

Make sure you always pay off your card balance in full every month, otherwise you might find it’s you who is in need of charitable support.

In the meantime, scout around the staffroom for Lycra-kitted colleagues readying themselves for the gruelling 26 miles of the London Marathon and dig deep into your pockets. And remember to tick the Gift Aid box

www.london-marathon.co.uk www.justgiving.com.