More than 34,000 telephone and at least 900 broadband subscribers in parts of the West Midlands were affected after burglars broke into a postal sorting office and cut the cables to a British Telecom exchange behind the building.

The raiders left emptyhanded. BT and the police are investigating whether they snipped the wires to make sure that no one could raise the alarm as they fled, or whether it was just another mistake.

Subscribers were told that in the event of an emergency they should use their mobile phones or raise the alarm via passers-by, neighbours or shopkeepers who had working landlines or mobile phones.

The emergency services also suggested that residents could contact them directly by visiting police stations to ask for help or using the emergency telephone boxes outside their local fire stations, which were still working.

West Midlands police said that callers should use their mobile phones to reach the force’s switchboard and say that they were dealing with an emergency.

The areas affected included central Birmingham, Aston, Perry Barr, Handsworth, Ladywood, Blackheath, West Bromwich, Tipton and Wednesbury.

BT said that the service was affected partially in some areas, but lost completely in others. The service also hit at least 900 broadband customers.

The burglars broke in to the Handsworth sorting office at Soho Hill on Saturday night. Police have not revealed how they entered but confirmed that they cut cables that ran to the telephone exchange behind.

At first BT thought that about 17,000 customers had been affected but, as the day wore on and engineers worked to patch up the network, the numbers began to climb and by last night the total had reached 35,700.

BT said that engineers were working around the clock to restore services.

A spokeswoman said: “These were major cables, so it’s a major repair job.”

By yesterday evening the engineers had managed to connect about 3,000 customers, but BT was predicting that the full service would not be restored until this afternoon at the earliest.

Police appealed to local radio, television and newspapers to report the breakdown so that customers understood why their telephones were not working.

A spokeswoman for BT said: “It’s a serious incident for us. We are investigating, but we don’t know why it was done.”

She said that there was no suggestion that the burglars might have been aiming to steal the cables. There is a high market price for copper, which is used for many types of electric cable.

Earlier this year some electricity companies gave warning about attacks on sub-stations, where thieves were stripping out copper and leaving areas without power.

Mail sorting offices can be targets for thieves who are looking for parcels or recorded letters, which often hold valuables, cash or even credit cards.

In Birmingham the burglars chose the only night of the week when there were unlikely to be any staff on duty, since there would be no deliveries on a Sunday.

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