Cameron's half-hearted commitment to families will be exposed by a group of Christian MPs today as an "impact on families bill" receives its second reading.

The bill attempts to force ministers to assess the impact government policies will have on families. It has been tabled by the new Christian MP for Eastbourne, Caroline Ansell, and is supported by several other Christian MPs including David Burrowes, Fiona Bruce and Jeremy Lefroy.

The effect of the bill will be to expose David Cameron's failed promise "to do everything we can to support family life in Britain today."

The Prime Minister announced "the family test" in August 2014 which he said would require "every single domestic policy that government comes up with to be examined for its impact on the family."

It has subsequently become clear that this supposed commitment is largely being ignored. Due lip service has been paid by ministers when the matter has been raised, but in reality the promise to consider families in "every single domestic policy" has been sidelined. Departments have hidden behind the excuse that there is "no requirement" to publish assessments and insist they are made in private.

Nevertheless, legislation that would bring obvious hardship to families – such as the reform to tax credits, placing a two-child limit on families receiving the in-work benefit – has been attempted.

CARE, a Christian policy charity which has supported Ansell in tabling the bill, said "there is a huge amount that still needs doing" to support families.

"It is extremely unfortunate that the Prime Minister's own family test has been largely ignored by government departments," said CEO Nola Leach.

"Family breakdown is costing the Treasury £47 billion each year and if any other problem was causing the Treasury to lose so much money, you can be sure everything would be done to guarantee government policy was not making the situation any worse.

"Families are the best safety net we have and are able to help children and other vulnerable adults in ways the State simply cannot."

Today's bill would make the family test a mandatory obligation of all government departments and ministers. The effect of this would be to force ministers to fulfill Cameron's promise.

However it is almost certain the bill will fail as it will not have government support. The effect of this will force the government to concede its failure to live up to the commitment to families.

Ahead of the debate Ansell said the government had the power to "wilfully or otherwise strengthen or undermine family stability." She urged them to do the former.

"The bill will ensure that Ministers and departments recognise and make explicit the potential impacts on family relationships in the process of developing and agreeing new policy and new legislative proposals," she said. 

"The current proposal to further relax Sunday Trading Laws is a case in point, variously described as potentially, 'causing irrevocable damage to our lives as citizens' and 'the sacrifice of family life on the altar of profit'."

Although it is highly unlikely the bill will become law, it is not entirely a waste of time. It will put government failings under the spotlight and pressurise them to live up to their one nation, compassionate conservative brand.