Watford MP Claire Ward has been accused of “betraying” the thousands of constituents fighting for compensation after losing their pension funds.

Ms Ward agreed last month to sign up to an all party group of MPs supporting former investors in Equitable Life, many of whom saw their retirement plans ruined when the company came close to collapse in 2000.

However, angry campaigners have now accused her of reneging on her earlier promises and “deceiving” the estimated 9,000 victims in her constituency.

Stuart Pole, chairman of Equitable Members Action Group (EMAG) in Hertfordshire and Middlesex, said the Labour MP reneged on the pledge at the end of March, when she voted against House of Commons motion that, its Conservative and Liberal Democrat backers claimed, would have brought full compensation a step closer.

Mr Pole, of Radlett, said: “We deeply regret Ms Ward's behaviour in this matter also now includes deceiving Watford constituents by undertaking to support them and then betraying them.”

Mr Pole also expressed frustration at Ms Ward’s lack of cooperation with the group on individual cases.

Liberal Democrat parliamentary candidate Sal Brinton, whose party supports full compensation, added: “This motion would have been a major step forward. I am disappointed and outraged at her failure to support 9,000 constituents.”

A spokesman for Ms Ward, however, dismissed the claims as “absolutely ridiculous and wrong,” adding that she was now dealing directly with constituents affected by the case – constituents whose details she could not discuss with a third party for reasons of confidentiality. Ms Ward would, he added, continue her support for victims to the best of her ability. More than one million Equitable Life policy holders have lost money. A Parliamentary ombudsman ruled in 2008 that the crisis occurred as a result of regulatory failings and told the government to apologise and pay full compensation.

Ministers, however, have only proposed ex gratia payments to those “disproportionately affected” – a process that avoids the acceptance of blame and raises, EMAG claims, the possibility of means testing.

Labour’s chief secretary to the treasury Liam Byrne, however, said in February that such a course of action was “neither desirable nor administratively feasible”.

EMAG is demanding full compensation.