Stewart McMaster, 34, now of Ingleby Crescent, Lincoln, admitted unlawful wounding on December 29, 2007.

Simon Rowe, prosecuting, said earlier McMaster had been at Claire Bradford's home in Walcott, but left when the 17-year-old boy and a 16-year-old arrived.

McMaster, who did not get on with the pair, went to a nearby pub, but on returning home found Ms Bradford in tears claiming one of the lads had stolen her mobile.

McMaster went to the home of the younger boy and after Ms Bradford raised the issue of the phone McMaster punched the 16-year-old in the face.

The 17-year-old intervened but was then attacked himself.

"He felt a tap to his lower back and realised that there was blood coming from his body," Mr Rowe said.

"He'd been stabbed. It was then that he noticed that the defendant had a large kitchen knife with a seven-inch blade in his hand."

The 17-year-old was taken to hospital where his back wound was repaired with three stitches. The younger boy suffered a cut lip but no serious injury.

McMaster left and later handed himself in at Lincoln Police Station admitting he had been drunk after downing half a bottle of vodka and more drink in the pub.

Recorder Phillip Matthews told him it was tragic that McMaster was before him: "It is because of your fondness for drink. Knives and alcohol are a potentially lethal combination."

Richard Marshall, defending, said McMaster had no previous convictions for violence and was remorseful.

He said McMaster reacted after arriving back from the pub to find his ex-girlfriend crying and claiming to have been manhandled before having her phone stolen.

McMaster's relationship with Ms Bradford is over, said Mr Marshall, and he has since moved out of Walcott.