Computer hackers are running up crippling bills by tapping into other people's phone lines and dialling sex-lines.

The impact of the hackers' actions is not only financial though. Families across Sussex have told how the appearance of the premium-rate numbers on itemised bills has threatened to destroy their relationships.

Lewes MP Norman Baker believes the scale of the problem is becoming so serious he is planning to raise it in the House of Commons.

But BT insists all customers are responsible for their own lines.

Joanna Read-Watson, 27, and her husband Darren say they are victims of the hackers who came close to ruining their life together.

Mrs Read-Watson said: "On one phone bill, I was in hospital giving birth to my daughter Eloise at the same time these calls had been made. I didn't know who was phoning these 0898 or 0906 sex lines.

"My usual bill was under £100, but this was for about £250. BT said that it must be someone in the house, that is, my husband Darren.

"They started to sow the seeds of doubt in my mind. I started to think it was him, and it put a tremendous strain on our relationship as we had only been together for 18 months."

The couple from Lexden Court, Seaford, had a series of arguments about the bills.

Mrs Read-Watson said: "We found out that some of the calls were to gay lines. I even started to think that he was homosexual. It started four years ago and it was very painful.

"After I had given birth, the last thing you need is to argue and be paranoid. We had many arguments over it and on several occasions Darren stormed off and didn't come back for hours.

"He was really annoyed that I could ever think he would do such a thing."

For six months, the couple argued over the bills. Even when they moved house, the phone calls continued. On one bill, a phone call to a lesbian line cost £86. Whenever they tried calling BT, they were told that it was not their problem and they must pay up.

Mrs Read-Watson said: "It was embarrassing. I had to ask my mum to pay my bill as I couldn't afford it. Can you imagine asking your parents to pay for a load of sex lines?

"I couldn't believe it when the phone calls kept appearing at my new house. It was obvious someone else was using the phone. It only stopped when I paid for a premium rate barring.

"BT were very unhelpful. They said it was my fault and my liability - they refused to accept there were hackers on the line."

There are different types of hackers.

Contractors and engineers can hack into the system to make a call at the customer's expense.

There are also gangs of hackers who set up premium rate lines and then illegally tap into the customer's line and call the number.

Former senior BT engineer Bob Godsiff claims that everyone could be at risk He said: "It's a massive problem. I think the increasing use of casual, contract labour in the telecoms industry is largely to blame.

"It's reached epidemic proportions."

The Read-Watsons are not the only ones in Sussex to suffer.

Nicola and Philip Newman, from Maresfield, East Sussex, have been through a nightmare two years, which has only just finished.

In February 2000, they received a phone bill for £300, which is £220 more than their usual bill.

For the following three quarters, the bills were all more than normal. All the numbers were for chat or sex lines.

Mrs Newman, 34, said: "When we asked BT to trace the numbers, they couldn't do it. We refused to pay the bill as we never rung those numbers. Why would we phone sex lines?

"We kept querying the bills as we couldn't afford to pay them. On two different occasions we were never even in when the calls were made. We were on holiday in Weymouth for a week and running a stall on a village fete.

"We have witnesses for both occasions but BT did nothing."

The final straw came when BT blamed their children, Jack and Thomas, who were aged five and three.

Mrs Newman said: "That was the final straw. The bills had already caused quite a strain on the marriage, but this was a sickening insult. They reckoned that as it wasn't me or my husband then it must be the children.

"They said that the kids must be getting up late at night, sneaking downstairs, opening the stairgate, turning the computer on, logging onto the internet and dialling into these premium rate lines.

"The BT man told us: "You'll be amazed at what kids can do these days." For God's sake, they were only three and five.

"But we were going to be blacklisted if we didn't pay the bills. We have only just finished paying them off."

Liberal Democrat MP for Lewes, Norman Baker, is calling for an investigation into the matter.

He said: "It's quite clear that action needs to be taken. I shall be writing to BT and Oftel to ask them how many people they have been prosecuting. It's quite clear the consumer needs to be protected.

"It's quite clear that people are receiving enormous bills they haven't generated."

BT spokesman Eric Barr said: "Every complaint is thoroughly investigated. Customers can have confidence in their phone bill. Cases of unlawful access to lines is extremely rare."

*The above couples are appearing in a Meridian Focus documentary called "Cheatlines", which is being broadcast after News At Ten tonight.