Terminally ill patients given six months to live often survive for three years, official figures have revealed, fuelling fresh concern over euthanasia and assisted suicide becoming legal.

Patients who are given a prognosis of six months by their doctors are entitled to be fast-tracked onto universal credit.

But Department for Work and Pensions (DWP) data obtained by The Telegraph revealed that a fifth of those benefit claimants are living much longer than expected.

The disclosure, made under freedom of information laws, prompted palliative care medics to warn lives will be “tragically cut short” if Kim Leadbeater’s euthanasia bill becomes law.

The draft legislation, for which MPs voted in November, proposes granting people with six months to live – or less – medical assistance to die, given the approval of two doctors and a judge.

Hospital data previously indicated that doctors’ prognoses were wrong more than half the time, but this is the first government data to confirm the inaccuracy of NHS life expectancy estimates.