A power failure has caused chaos at a busy medical practice in Oxford as staff lost access to thousands of patients' records for more than 24 hours.

The cable fault outside Marston Medical Centre in Cherwell Drive, Marston, happened as doctors and staff returned from the Bank Holiday break yesterday.

With the electronic switchboard dead, the practice was cut off to anyone wanting to see the three GPs or two practice nurses. Being fully computerised, staff had no record of who had already been booked in for appointments.

Within minutes of staff arriving, the lights flickered and then went off completely.

Staff then heard a rumbling sound coming from beneath them, and decided to evacuate the building after detecting an acrid smell.

Southern Electric engineers discovered that a joint in the cable outside the centre had blown, leaving the underground cable smouldering for hours.

The engineers called in a digging crew to reach the fault and spent the rest of the day trying to repair the cable, only to have it blow again when power was reconnected.

Workmen stayed at the scene until 2am today, and returned at first light to continue. A spokesman said it was hoped that full power would be restored today.

Wendy Greenberg, practice manager, said: "We've been without power for 24 hours, with no access to the 4,400 patients we have in Marston, Headington and north Oxford.

"It's hard to know the scale of it really, but the day after a Bank Holiday is usually very busy.

"We have no access to patients' records or prescriptions, and although we have some pre-booked appointments, we don't know what they are for. We're just sitting here waiting for people to turn up."

Ms Greenberg said anyone telephoning would hear a permanent ringing tone, as calls were not being automatically diverted.

Southern Electric gave them a small generator, but the power was insufficient to keep vaccines at the proper temperature. These were placed in the fridge at a nearby patient's home until power was restored.

Ms Greenberg said: "We're very sorry that people haven't been able to get hold of us, and just hope that if anyone was ill, they managed to dial 999 or their GPs."