TELECOMS giant BT is staying tight-lipped over how a fire at its exchange in Derby knocked out phone lines of tens of thousands of customers, including Rolls-Royce and Toyota.
The blaze happened at 3.30am yesterday, but some customers did not get back their service until the afternoon.
BT said "the majority" of customers were back on by 2pm.
The firm apologised for the disruption but could not say how the fire started, why it caused such major problems and what measures would be taken to stop it happening again.
A spokesman said: "We have been investigating the damage. Engineers have been doing everything possible to get these services fixed as quickly as possible and the vast majority of those line affected were repaired within a few hours. We apologise for any inconvenience.
"The exchange contains equipment which connects individual phone lines in Derby into the national and international network."
Former BT telephone engineer Paul Cable said that the damage caused by the fire would have been catastrophic due to the number of wires in the small space at the exchange.
Mr Cable, of Derby Telephone Diagnostics, said: "There's a room at the Derby telephone exchange that's about the size of a tennis court where all of the wires for Derby's telephone service meet.
"Once a wire is burnt then it will need to be replaced and there's the risk that fire and burglar alarms do not work until they are replaced.
"Each line has a pair of wires so if tens of thousands of people have been affected then that's a hell of a lot of wires that have been replaced.
"There would probably have been a team of people working hard to reconnect everybody and I expect that over the next few weeks there will be one or two irate customers still having problems.
"There is no back-up if the Derby telephone exchange is out of action. Telephone lines are connected to central hubs where all landline calls for a particular area are handled. If a line goes down, it is quicker and easier to repair the problem rather than reroute it to another exchange."
The fire service said the cause of the blaze was still not known.
The BT spokesman was unable to say if the building had smoke alarms, a fire alarm or a sprinkler system.
He was also unable to say if affected customers would get compensation.
The early-morning blaze meant lines across the Midlands were put out of action as engineers spent the morning and early afternoon attempting to repair the damage.
The fire happened at the BT exchange in Colyear Street, in Derby city centre. Two small blazes started on the first floor of the building and damaged telecommunications equipment and cables.
No one was in the premises at the time but enough damage was done to wipe out phone lines to areas all around Derbyshire, as well as parts of Staffordshire and Warwickshire.
A spokesman for BT said yesterday morning that the fire was not being treated as suspicious.
He said: "One thing that is clear is it has affected tens of thousands of people in and around the Derbyshire area.
"We do not yet know specifically which areas have been affected but hopefully this will become clear throughout the investigation.
"At the moment we are not treating it as malicious or suspicious."
Many of Derby's biggest businesses and services were affected by the phone blackout.
The Royal Derby Hospital was one of the main centres to suffer from the problems.
Paul Brooks, director of facilities at Derby Hospitals NHS Foundation Trust, said: "As a result of the fire at the BT exchange we were unable to take incoming calls directly to wards and clinics throughout the Royal Derby Hospital this morning.
"However, our main phone number was fully functional and we brought in extra staff to handle the increase in call volumes.
"Because of this, the overall effect on both staff and patients in the hospital was very limited and by midday the system was once again operational.
"We apologise to anyone who did experience any inconvenience throughout the period."
A hospital spokesman said: "As a result of the BT exchange fire overnight, the majority of our incoming phone lines at the Royal Derby Hospital have been affected, which includes lines into wards and clinics.
"We want patients and relatives to be aware that they may experience difficulties in trying to get in touch with the hospital and we ask that people bear with us while the issue is resolved.
"Incoming phone lines into the London Road Community Hospital are working as usual."
Rolls-Royce also experienced issues with its phone lines throughout the day.
A spokeswoman said: "I can confirm we are experiencing disruption at our Derby site like everyone else.
"We have been in contact with BT and will continue to be until the problem is fixed."
Interfleet, in Pride Park, was another company that suffered as a result of the blaze.
Communications manager Sherrie Rowlands said: "Our phones have been down. I have been leaving the IT guys, who are in contact with the BT engineers, to try to sort the problem out."
External phone lines into Toyota's Burnaston plant were affected.
A spokesman for the car manufacturer said: "We have had an e-mail round this morning from our IS department informing us that there is an issue with the external line coming into the offices.
"Our internal lines, e-mails and internet are unaffected and we are working as normal."
A spokesman for Raynesway packing firm Davpack said its services were restored at 9.50am. He said: "We are very relieved that BT has responded so quickly to restore the phone lines.
"As a mail order packaging business with customers around the UK, our phone connection is essential to the running of our sales office and for payment processing.
"Whilst our website is available to customers 24/7, many customers have special order items, or seek advice on their packaging, so we see a big impact when the phones go down."
BT apologised for the inconvenience caused to the network's users. Spokesman Paul Hayward said: "Some households and businesses in the Derby area saw a loss of telephone services this morning following a fire at one of our exchanges.
"A large number of those customers affected have already seen their telephone service restored and we expect the remainder to be back up and running shortly."
