Almost 30,000 properties were left without electricity on Monday as a power cut hit Truro and the surrounding area.

The entire city was blacked out from 9pm to 9.30pm, along with St Agnes, Perranporth and the Roseland Peninsula, after an insulator failed.

The insulator had been damaged in a previous lightning strike, and abruptly gave out causing the whole network to shut down. Homes all over the South West also experienced some fluctuations, though none outside the Truro area lost power.

Tracey Carr, a spokeswoman for Western Power, the company responsible for the city's power supply, said 28,973 properties were affected and repairs to the insulator were ongoing.

She said: "Previous lightning damage had weakened the insulator and repairs are underway. It has now been proved that there is no more damage."

But this will be small comfort to restaurant owners in the city, who watched in dismay as their customers walked out after being plunged into darkness.

Vicky Caruana, head waitress at Piero's restaurant, on Kenwyn Street, said: "The lights kept going out and coming on until they went out completely. Customers weren't impressed. We couldn't cook because there were no lights in the kitchen and we couldn't even make coffee because the machine is electric.

"People wanted to pay but couldn't because our card machine wasn't working and they didn't have any cash. They had to go out and leave their cards behind."

Carrick council's computer system was also affected after one of the servers made a faulty shut down.

Technical staff were still trying to revive the system yesterday, although a spokesman said none of the core systems - including benefits and housing - had been affected.

At the Royal Cornwall Hospital, back-up systems prevented a serious tragedy, but the telephone system was briefly affected and some lifts temporarily jammed.

A spokeswoman for the hospital said: "There was some interference with telecommunications and the power supply. However, our back-up generators swung into action very quickly and teams from estates and IT were immediately on hand. Staff dealt very well with the problem and everything was back to normal by 11.30pm."

Not so for Truro firefighters who had an unusually busy night attending hundreds of properties where automatic fire alarms had been activated. Among them were Truro College, Treloweth School and Carrick district council's Kernow House. No casualties were reported.