So frustrated was David Cox by a wall of silence facing him at British Gas over a claimed bill and £20,000 in legal fees, the Isle of Dogs resident wrote his own apology and asked the firm’s chief executive to sign it.

The letter describes “four years of misery” and begins “I would like to sincerely apologise for the appalling treatment you received from British Gas”.

David worked as a director for a company and his problems began after the energy giant starting pursuing him for a unpaid debt covering a period of two years after the company had left the building at the centre of the dispute.

David – fed up with repeated threats to enter his home – took British Gas to court for harassment.

The judge agreed with the company it had a right to chase for money and the east Londoner was forced to pay the costs of his own and British Gas’s legal teams, totalling £19,000.

However, weeks later Mr Cox was shocked to find out British Gas had already written off the debt, only to reactivate it for the trial.

David said he wrote the letter for the CEO in a bid to “get their attention”.

“I would like to sincerely apologise for the appalling treatment you received from British Gas,” said the letter, purportedly on behalf of the energy company.

“We chased you for years, falsely claiming you owed us thousands of pounds, when you hadn’t even been a customer of ours.

“We sent you scores of demands for payment – several every month, threatening forced entry to your home with police, dog handlers and bailiffs if you did not pay up.

David Cox, an Isle of Dogs resident, who has written his own apology letter for British Gas to sign after years of harassment. For use: Louisa Emery

“I can see that we were told that you were occupying their building to which we supplied energy. We fell for this hook-line-and-sinker even though we checked the Land Registry and found you were not the tenant.”

British Gas admits it said it had ‘written off’ the debt before the case but insists this meant it had passed it on to a debt recovery company.

In a statement it said: “Mr Cox brought a claim against British Gas for harassment which was dismissed by the court. In an effort to draw a line under the matter, we then decided not to pursue further debt recovery action against him.”

In response, David said: “They might well want to ‘draw a line’ under their erroneous chasing of me, but they haven’t drawn a line under the damage they caused by doing it. It’s very frustrating that they just dismiss the issue without any explanation or being held to account.”

The British Gas CEO is yet to sign the letter.