Gordon Brown has launched a consultation on how to fund social care for an ageing population, with a promise to build a "fairer Britain".

The prime minister said that without radical reform the system in England faces an estimated £6bn funding gap within the next 20 years.

His speech to the King's Fund in London begins a six-month consultation focused on making care services fairer and affordable.

Brown said the current system of means-testing could seem unfair, with many families anxious they would have to sell their homes or other assets to pay for care.

He is proposing new measures to allow people to save for their old age while protecting their homes and inheritance.

He said he wants care to be more responsive to demands for independence, and it should be easier for people to stay in their homes.

"This is an issue at the heart of our ambition to create a fairer Britain," he said.

"Of course, helping relatives is a challenge that most families rise to - however difficult it becomes.

"But that doesn't make it any easier. Nor does it remove family worries about providing physical care that is needed - or take away people's concerns that at some point in the future they may have to sell a treasured home to pay for their own care.

"It is essential that in future there is fairness for those who work hard and save for their retirement."

Health secretary Alan Johnson also launched a £31m pilot scheme which will see elderly and disabled people use automated safety devices to help them remain in their homes for longer.

Speaking on BBC Radio 4's Today programme, Johnson said: "There is no quick fix here and I think people on all sides of the House recognise that.

"On the one hand, we have to ensure that people receive a high quality of care.

"We have to ensure that those people who have put money aside, who have scrimped and saved, are not adversely affected that the system doesn't treat them unfairly.

"And we have to ensure that the system is affordable, not just for individuals but for the whole country."