Former prime minister Gordon Brown has branded the move to means-test free TV licences “the wrong decision”.
The BBC announced plans to make the concession available only to those receiving pension credit, but Mr Brown said the Government should foot the bill without threatening BBC services.
He said: “This is a clear breach of an election promise that was made by the Conservative Party that the licence fee would remain free to pensioners over the age of 75 for the duration of the parliament.
“This is the wrong decision, made in the wrong way by the BBC.
“It should not be an agency for means-testing pensioners. Any costs should be covered by the Government without endangering BBC services.”
The former Labour leader wrote to the BBC during its consultation on the future of the concession, the cost of which it inherited from the Government as part of its new charter.
He warned that pensioners who could not pay for the licence could become criminals after years of enjoying the concession.
Mr Brown criticised the idea of an unelected body being given the power to decide the distribution of benefits.
He wrote: “We have to ask whether, after 20 years of free licences, the BBC can justify taking a frail, housebound, elderly pensioner to court for not possessing a TV licence that for years she has had for free, and then not only having the power to ask for a fine of £1,000 – the standard penalty – with legal costs on top, but also to have the power if she doesn’t pay or can’t pay, to ask the courts to send her to prison.”
His warning was echoed by Labour MP Barry Gardiner, who told the BBC: “Can you tell me how, after 20 years of free TV licences, the BBC could justify taking a housebound pensioner to court if they could not afford a TV licence?”
Scottish National Party MP Hannah Bardell also raised concerns, writing: “It’s a shocking fact that dozens of people, many of whom are women, are sent to prison every year for non-payment of their licence.
“As if this is not bad enough, to potentially prosecute people in their 80s and 90s and send them to prison for not being able to afford a TV licence is absolutely unacceptable.”
About 3.7 million pensioners are thought to be ineligible for the concession, with around 1.5 million households able to claim it.
The BBC said shouldering the financial burden of free licences would have forced the broadcaster to cut major services.
Changes will come into effect in 2020.
The free licence fee was introduced by a Labour government in 2000.
Under the Conservatives in 2015, ministers announced that an agreement had been reached between the Government and the BBC, and the broadcaster would bear the cost.