LONDON - Four Britons have committed suicide with the help of doctors at a Swiss clinic in the last six weeks, a British voluntary euthanasia pressure group said to highlight their call for a law change.

Dignity in Dying said the deaths bring the number of Britons who have travelled to the Dignitas clinic in Zurich to end their lives to 54.

At the same time, the group said more than 800 Britons were now registered with the clinic -- about 100 more than in January this year -- and predicted British membership could top 1,000 by the end of the year.

Dignity in Dying's chief executive, Deborah Annetts, said she was "shocked and saddened" by the latest deaths but each case demonstrated the need for a change in legislation to make assisted suicide legal in Britain.

"These cases are gathering momentum and a signal is being sent to the British public that if they can afford to go abroad to die, that's no problem," she said.

"But if you have such help here your relatives could face 14 years or life in prison."

Assisted suicide -- when a patient is given drugs by a doctor and takes them themselves -- is illegal in Britain but the issue has gained more prominence in recent years because of Britons travelling to Switzerland.

So-called "passive" euthanasia is legal in Switzerland: doctors can supply lethal drugs to terminally ill people but not adminster them.

In January this year, a British woman with the same incurable degenerative brain disease that killed the actor and comedian Dudley Moore took her own life at the Dignitas clinic to avoid a long, slow death.

Beforehand, retired doctor Anne Turner urged British Prime Minister Tony Blair's government to make it easier for the terminally ill to end their lives with proper medical help in the comfort of their own country.

But the medical establishment is against any law change for doctor-assisted suicide and voluntary euthanasia -- when a patient may need the drugs administered because they are too ill to take them themselves, or when they choose to have a doctor administer them.

Discussions on a proposed law change put forward by the former human rights lawyer Joel Joffe in Britain's upper chamber of parliament the House of Lords in May were postponed for six months in June this year.