A naked British soldier jumped out of his bed, ran out into the street and smashed a car window with his bare hands to stop a knife-wielding thief from stealing his girlfriend's car, reports say.

Lance Corporal Wayne O'Mahoney, 41, a veteran of the Iraq war, was asleep about 6am on Saturday when he heard banging in his home in the neighbourhood of Salford in Greater Manchester, north-west England, the Manchester Evening News reported.

"I was curled up asleep and I heard the banging. I couldn't believe what I was hearing," Lance Corporal O'Mahoney, of the 103 Regiment Royal Artillery, told the Evening News.

"You couldn't print what was going through my mind. My home is my castle and you can't just intrude and expect to get away with it."

Lance Corporal O'Mahoney said he ran downstairs and tussled with three men, who were wearing balaclavas. Two ran out of the house, but one grabbed his girlfriend's car keys and jumped into the car, which was parked outside on the street.