At least £2bn of the NHS budget should be used to meet the costs of social care for older people in a move that it is claimed would ultimately save the health service money, according to an influential backbench Tory MP.

Heather Wheeler, a member of the Conservative 1992 backbench committee and chair of the all-party group on local government, warns that the scale of the challenge facing councils in providing social care means the NHS budget must be re-examined to meet the current funding gap for social care. The shortfall is set to rise as the population ages.

Her call comes ahead of the Queen’s speech on Wednesday in which the coalition will lay out its plans to address the boundary between NHS acute care and local government-funded means-tested social care in a care and social support bill.

The new legislation is also designed to show that the Conservatives are listening to disaffected voters who strayed to Ukip in the local elections last week. It will contain populist measures to limit benefits to some immigrants with a particular focus on placing restrictions on access to the NHS. The legislative package will also include measures to prevent people who live overseas and have not contributed national insurance from claiming a pension based on their spouse’s contributions.

On social care, Wheeler said that taking money from the health budget would reduce the need for costly medical interventions – and that there would be cross-party support for the measure.

The former Liberal Democrat social care minister Paul Burstow has also called for a further shift, saying: “There is now a strong case to ringfence the extra social care funding. At the moment there is a danger that we are pouring water into a bath with the plug out. Too many local authorities are not using extra funds for social care for what it was intended. It is something the spending review needs to address”.

The social care bill was being presented by Downing Street on Monday explicitly alongside parallel changes designed to introduce a flat rate pension of £144 a week from 2016. The biggest group of winners from the pension and care changes will be women, a target group the Conservatives badly need to win back if they are to win the 2015 general election.

Wheeler said: “Local authorities tell me time and time again that meeting the current and growing demand for social care support for older and disabled people is the single biggest challenge they face. The warnings are there that we must address this immediately.

“Using funding from the NHS ringfence to provide appropriate social care is the most sensible option available to the government. What’s more, funding preventative social care will actually save the NHS in the long term. This is a win-win situation for the government.”

The joint select committee that examined the draft care and social support bill, chaired by Burstow, warned that the boundary between the acute and social care was poorly drawn, and local government could find itself under perpetual legal challenges if it was not made clearer.

The wider the gap in social care funding grows the more it will destabilise a fragile system, and jeopardise the vision of the government’s social care reforms, Burstow argued.

He said: “Without greater integration, particularly with health and housing, the care and support system will be unsustainable.

“There is a growing need to join-up services so they fit around people’s lives and make the best use of resources. I think the government will act on that. The whole system must shift its emphasis away from crises and towards prevention and early intervention.”

Burstow’s joint committee also proposed the draft bill be amended to give ministers power to mandate joint budgets and commissioning across health, care and housing, such as support for the frail elderly, making it simpler for NHS and local councils to pool budgets. Pooling should be the default option, he said.

He added: “It is an extraordinary omission that the Treasury had not undertaken any systematic assessment of whether extra spending on social care would reduce NHS costs. We should know how much an extra £1 spent on social care saves the NHS budget.”

Burstow is also expecting proposals for a duty of candour to be imposed on social care staff parallel to the one for NHS staff. Staff would be duty bound to report serious incidents of failure.