Most GPs work in practices with one or several other colleagues, all of whom could be the first to spot performance failures, or something more sinister.

But when the doctor works alone that first line of scrutiny does not exist and, as the Shipman case shows, problems can go undetected for many years.

So what is to prevent other solo doctors, known as single-handed GPs, going on their own killing sprees?

Nobody could have spotted what Shipman was going to become

GMC

Those responsible for regulating the medical profession argue that what happened in Hyde could not happen again because of the checks now in place. They say that not only is Shipman a one-off, but a series of measures introduced to pick up on failing doctors would now uncover those who are corrupt or plain evil.

One of the government's key reforms in the family health sector has been the introduction of primary care groups (PCGs) which lump together doctors' practices within an area, combining reponsibility for providing services.

The era of a minority of GPs working in splendid isolation is, therefore, over, says Dr Simon Fradd, chairman of the Doctor-Patient Partnership and deputy chairman of the British Medical Association's committee for GPs.

Clinical governance

Each PCG is also responsible for clinical governance - the term given to performance assessment now being carried out on all GPs and hospital doctors.

This, it is argued, brings single-handed GPs under a collective assessment of their work which should unearth wrong-doing.

"The reorganisation of the health service and the role of clinical governance means that doctors can no longer work in total isolation," said Dr Fradd.

The key responsibility for ensuring doctors are up to scratch remains with the General Medical Council (GMC), which claims procedures now in place would prevent a repeat of the Shipman case.

Dr Simon Fradd: 'Doctors can no longer work in total isolation'

The GMC says in particular that Shipman's previous drug conviction, for illegally prescribing in the 1970s, would be treated very differently today and that major changes have taken place in regulation during the past 25 years.

"The history of Shipman is one that goes, in terms of known problems, back to the 1970s. Nowadays the problems he has had with drugs would be treated very differently," said a spokesman.

Conditions are put on their registration and if they do not follow them, they are suspended. They then come under the supervision of a medical assessor, who reports to the GMC on whether they are fit to practise. After two years they are suspended indefinitely and removed from the medical register.

The GMC's role is also set to expand when, in May 2001, it introduces a process called revalidation, under which doctors will undergo periodic scrutiny of their skills by their peers, possibly at five-yearly intervals.

Questions have also centred on the issue of the death certificates signed by Shipman for the patients he murdered. Only one doctor's signature is needed for burial, while two are required when the dead person is to be cremated.

A spokeswoman for the Office of National Statistics, which is responsible for death certificates, said: "Two doctors would be required to sign separate medical certificates for causes of death with cremation. That would be a sort of safeguard."

Death certificate

But Dr Fradd says the problem is more deep-seated than the number of doctors signing the death certificate and the high death rate should have been picked up somewhere in the system.

He says a wide-ranging inquiry is needed into all aspects of the case, including the issue of death certification.

"We need a public inquiry to look at what went wrong and how they could be detected. Its conclusions should be implemented immediately to restore public confidence."

But there is a warning that picking up exceptional cases like that of Shipman will always be difficult. The GMC spokesman said: "The bottom line is that nobody could have spotted what Shipman was going to become. There will always be very rare cases in all walks of life where future conduct could not be anticipated."

And Dr Fradd adds: " We have to bear in mind that in this case we are dealing with a psychotic. You can try and set up a system to deal with that but you can never make it 100%."