The recent documentary on the mass murderer Dr Harold Shipman brought back unpleasant memories.

If the public could not understand why an apparently caring GP was murdering his patients, neither could I.

As the news filtered out that a GP near Manchester might be killing his patients, my first response was of disbelief.

There was clearly a witch hunt against my colleague. Was he well-meaning but misguided; committing euthanasia rather than letting people suffer?

As it became clear that he was an arrogant mass murderer, I felt compassion for his victims and anger that anyone doing my job should abuse his position in such an appalling way.

It was another GP and the local funeral director who first became suspicious. Why did he have so many deaths and why were they often in the afternoon when he was present?

They notified the coroner who arranged a confidential police enquiry. Nothing suspicious was found.

His last murder was unlike the others. Kathleen Grundy was found death at home in 1998. He forged her will claiming that she left him £386,000. The forgery was obvious, poorly spelt and typed on his own typewriter.

Mrs Grundy’s daughter was a lawyer. He had also backdated consultations on his computer unaware that the actual date information is inputted on a computer can easily be traced.

Having literally got away with murder throughout his career, why did he make this crime so obvious?

We will never know how many people he murdered but it must be several hundred.

One of the medical journals published the number of death certificates he signed in a year. I then went through my death certificate book. He had signed many more death certificates in a year than I had. I’m not such a brilliant doctor that I can save far more patients than a colleague.

Even taking into account the age of his patients this cannot be easily explained.

He was also extremely arrogant, believing that his intellect was superior to ‘simple policeman’. When finally convicted, he was proved wrong.

The first response of the Government was to set up an inquiry. We must, they argued, regain the public’s faith in GPs.

In fact, before Shipman surveys put doctors top of all the professions with about 90 per cent approval.

After the case public opinion did not change. The public knew that he was an evil murderer who happened to be a GP.

As one journal suggested, we do not criticise all artists because Hitler was an artist.

The difference is that Hitler did not use his position as a failed artist to become a psychopathic dictator.

Shipman used his position as a GP to kill people.

After Shipman, we faced many changes.

Although many of these were improvements, they would not have stopped another Dr Shipman.

They were designed to ensure high standards. There was no suggestion that Dr Shipman was incompetent. He was an excellent doctor, which is how he literally got away with murder.

All GPs must now face annual appraisals from a colleague, they must all carry out at least 50 hours of study to keep up to date and carry out regular audits of their work.

I was appointed as an appraiser but found that, after assessing local GPs I usually came away feeling guilty. Most were doing far more than I was, maintaining very high standards.

There are also much tighter restrictions on ‘controlled drugs’; drugs such as diamorphine (heroin) which he used to murder patients. Every prescription must be carefully documented. No-one could argue with these rules.

Another proposal which was not implemented was to have two coroners, one medical and one legal, to investigate all deaths.

This was clearly impractical and very expensive, although I quite fancied the job of medical coroner.

So how can we stop another Shipman? Just realising that it is possible is a safeguard. Shipman got away with murder because no-one thought such evil possible.

Also, in hindsight there were many suspicious statistics; deaths when the doctor was present, deaths in the afternoon or the amount of diamorphine he was using.

The Shipman case changed general practice ensuring higher standards and more accountability. Perhaps some good came from evil.