Authorities in Switzerland look set to bring in new controls to regulate the assisted suicide organisation Dignitas after questions are raised about its transparency.

Public questions about whether the organisation's founders make money from offering medically assisted suicide have begun to arise as the authorities discover urns of ashes in Lake Zurich.

The authorities were already considering bringing in a law to make it harder for foreign nationals to end their lives in the country.

Assisted suicide is permitted under Swiss law, as long as those involved in it are not selfishly motivated and do not make a profit.

The Swiss widely believe that end-of-life decisions are the preserve of the individual, and not the government.

But concerns are now emerging at the numbers of non-Swiss who are travelling to the country to end their lives.

The 1070 people that the clinic has helped to die since it was founded in 1998 have included an estimated 100 or more UK nationals.

Around 85% of Dignitas' clients come from beyond Swiss borders, with the largest national group hailing from Germany, then the UK, then France.

Dozens of urns containing human ashes and bearing the mark of the cemetery used by Dignitas were recently hauled out of Lake Zurich.

Some allegations have suggested a link to the services provided by Dignitas, with suggestions that the final wishes of clients may not have been honoured.

Dignitas whistleblower Soraya Wernli has claimed that she was present when urns were dumped in the lake. Wernli said she resigned from the organisation in 2005 after she felt it had become too profit-oriented.

However, while Wernli said she still supported the right to choose one's moment of death, she has assisted police with their enquiries into the matter.

Dignitas founder Ludwig Minelli has declined to comment on the urns, which are still under investigation.

He said there was no reason for Dignitas to show greater transparency because the group did not use public funds to carry out its work.

He said internal guidelines at Dignitas dictate that the organisation will never precipitate an assisted suicide. Every step of the process must be initiated by the person seeking to end their life.

Clients pay a membership fee of around £133, followed by a further £53 in annual fees. The cost of the assisted suicide can be as much as £4,700, including consultation fees.

It is thought, however, some clients may have donated much more than that.

Minelli declined to comment on allegations that he has become rich through Dignitas' work, saying that only the group's active members had a right to know the facts.

The active members are Mr Minelli, and one other who prefers to remain anonymous.

Doctors at Dignitas said they were willing to provide services to those with chronic debilitating illness, and mental illnesses such as schizophrenia.

Among their clients have been a young rugby player paralysed in an accident and a Spanish man with paranoid schizophrenia.

However, the government has said one of their doctors is not qualified to prescribe for the mentally ill, a decision which Dignitas is challenging in court.

Two forthcoming Swiss government draft papers on assisted suicide are expected soon, one proposing banning the practice, and the other limiting it to the terminally ill. The second is judged more likely to be approved by parliament.

Under the new rules, patients would have to provide evidence from two independent doctors that their illness is incurable, that they have only months to live, and that they have made an informed and considered  decision to end their own lives.

Currently, Dignitas' foreign clients are likely to arrive in Switzerland, see a Dignitas doctor and die within 24 hours.

But any change to existing Swiss law is likely to be a long process, and Ludwig Minelli has vowed to fight for people's right to make a decision regarding their own death, and to push for a national referendum on the subject.