A Tory who served as a health minister in the coalition government has launched the latest attack on government policy from its own backbenches, challenging the prime minister to make good on personal pledges and warning that it was increasingly difficult to justify putting “middle class tax cuts” before the needs of the poor.

Dan Poulter, a doctor working in NHS mental health services, said that he had been persuaded to enter politics in 2006 after meeting and listening to David Cameron talking about “broken Britain”, when the then leader of the opposition pledged to support what he described as “the victims of state failure”.

But in an article for the Guardian, Poulter said that he struggled to see much improvement in the situation of some of the most disadvantaged people in British society as he reflected on what had changed since his meeting with Cameron in 2006.

“When there is so much still to be done to improve the life chances of the most vulnerable, it is difficult to justify putting middle class tax cuts before the needs of the working poor, and the socially disadvantaged,” he added.

Poulter, who was elected in 2010 as the MP for Central Suffolk and North Ipswich, recalled first meeting Cameron during a period when the Tory party was moving towards what he characterised as “the more caring and compassionate image, which has more recently been repackaged as One Nation Conservatism”.

It was at Poulter’s invitation that Cameron visited a centre in East Sussex, at which the doctor volunteered some of his free time to care for people who were homeless, or living with severe and enduring mental illness.

However, Poulter said that some of the most disadvantaged people in society were still the people that politicians tend to forget, as he hit out at “chronic underfunding” of mental health and social care services, a shortage of social and appropriate sheltered housing, and a benefits system that he said did not always adequately recognise the needs of people with severe and long-lasting mental illness.

He added: “If we are serious about improving the care and the life chances of the most disadvantaged people in our society, we must properly fund and join up the many agencies and services that care for them.”

“This also requires a benefits system that properly support those with mental ill health. If we want to fix the ‘broken Britain’ that the prime minister identified, then there is still much to do.”