A Jack Russell enforces his own brand of justice to any customer who does not buy a drink at the pub where he lives.

Four-legged Jack patrols the Ship Inn, in Guisborough, east Cleveland, making sure regulars buy a drink.

He greets all comers with a wagging tail and lets them fuss and stroke him.

But woe betide any patron or tradesmen, who have not had a drink or a glass in their hand and want to leave.

For the five-year-old enforcer changes tack in a flash and won't let them out of the pub, occasionally growling and sometimes playfully nipping at their ankles to make his point.

Jack also has a go at people who sneak in to use the toilets forcing his owners, landlord and landlady Richard and Jean Storey, to put up warning signs.

Even the local postman keeps his distance, preferring to throw the mail through an open door rather than walk up to the bar.

Pub regular Ken Morgan, 55, said customers were safe as long as they bought a drink.

He said: ''It is phenomenal. Jack has not been trained to do it. He just does it and he has done it ever since he has lived here. He just doesn't like anybody not buying a round.''

Mr Storey said Jack, who the couple have owned since he was a puppy, was very friendly with children and other dogs.

''Nobody trained Jack to do it, he just brought it on himself,'' said Mr Storey, who has run the pub for nearly five years.

''No one can walk in and use the toilets and leave without buying a drink. We've had to put a notice on the door because of him.''