A teacher who used to weigh 42 stone is to run in the London Marathon this weekend after shedding more than half his weight.

Roberto Enrieu, from Coventry, used to struggle to climb a few steps until about four years ago when a colleague suggested he tried to lose weight.

Since then he has lost 25 stone and seen his waistline reduce from 66 inches (167cm) to 36 inches (91cm).

He said the race was another goal to aim for after losing so much weight.

He said: "If I look back at when I first started, if you had said to me that in 2010 you are going to be running the London Marathon, I would have said you'd need your brain looked at."

The head teacher of Longford Park Primary School in Coventry, where Mr Enrieu works as an ICT technician, first suggested he needed to lose weight.

He joined a local slimming group and started a fitness regime.

"I was nearly 42 stone," he said.

"You do realise there's a problem but like everyone who is overweight, you're very complacent about how you are and how you do things.

"Going up a flight of stairs was like conquering Everest for me - I'd get out of breath, I'd stop, get my breath back and carry on."

He now hopes to complete the marathon in under five hours, with all the money raised going to the NSPCC.