But when environmental health officers went behind the scenes at the Harvester in Portsmouth they were stunned to see how the filthy reality compared with the carefully-packaged brand image of the restaurant chain.

Responding to reports of a mice infestation, the officials could not believe their eyes when they saw the contents of a store room just off the pantry – piles of boxes, a ladder, an old bike and dirt everywhere.

The Harvester on Eastern Road, Portsmouth, has long been a favourite eating place but national company Mitchells & Butlers, which owns the chain, faces a hefty fine after admitting at Portsmouth Magistrates' Court to failing to keep the premises clean and failing to control mice properly.

Portsmouth City Council environmental health officers described what they found at the restaurant as 'filthy' and 'disgusting'.

They were forced to investigate after complaints from customers that mice were seen running about in the bar area.

The infestation got so bad that 25 mice were caught in a single night in May 2007.

The investigation in the summer of 2007 also found the restaurant's kitchen to be dirty, food on the floor, a carpet covered in thick grease and dirty wash-basin taps.

The steps from the kitchen to the bins and pantry were covered with grease and food, there was rubbish in the pantry, trodden-in dirt on the floor and mouse droppings and bits of food behind a sofa in the restaurant.

The case has now been sent to crown court for sentencing after Portsmouth magistrates felt that the offences deserved a greater fine than the maximum £10,000 they could impose.

Magistrate Sue Waddle, chairman of the bench, said: 'We represent Joe Public, and Joe Public doesn't care how many protocols are in place.

'Joe Public just wants to know a kitchen is clean and mice are not present.'

Paul Hunt, the city council's head of public protection, said: 'This conviction sends a clear message to the management that they must ensure their premises are maintained in a clean, hygienic and pest-free condition.'

Mitchells & Butlers spokesman Andrew Roache said: 'Food safety is our top priority and responsibility. We expect every employee to adhere to our rigorous documented food safety processes and any breaches are taken very seriously.

'These incidents happened some 15 months ago and we acted quickly to address them.

'We undertook a comprehensive review of all food hygiene practices at the restaurant to reinforce the high standards of food safety that we require.

'We have also put in place a new, highly experienced team, including a new restaurant manager and a new area manager.

'We have a long-established programme of regular, independent inspections of food hygiene standards in our restaurants so our customers can be assured that their meals are carefully and properly prepared, cooked and served.'

The Harvester was re-inspected by the city council in November 2007 and given a 'satisfactory' hygiene rating.