Imagine for a second the BBC taking a frail, housebound, elderly pensioner to court for not possessing a TV licence that for years she has had for free. Then imagine fining her £1,000 – the standard penalty – with legal costs on top; and if she doesn’t pay or can’t pay, sending her to prison.

Unthinkable? In fact, one in every 10 court cases is over non-payment of TV licences. And from next year, millions of people aged over 75 could lose their right to a free TV licence – and, if they don’t pay up, end up being taken to court despite a Conservative election promise they would not have to pay.

In a sheepish private message to the BBC a few days after their botched general election campaign of 2017, the Conservatives asked the corporation to simply ignore the fact that Theresa May had made a specific election promise to those millions of pensioners that they would continue to have a free TV licence. The Tories’ manifesto had stated: “We will maintain all other pensioner benefits including free bus passes, eye tests, prescriptions and TV licences, for the duration of this parliament.” The Conservatives told the BBC they had made a mistake by promising free licences until 2022, and insisted the BBC had the power to abandon them in 2020, thus overriding their election pledge. Even now, a year and a half on, the party has not levelled with the British public.

In a paper a few weeks ago, the BBC had to admit it might charge all of those not on pension credit a licence fee – and thus restrict the free licence to 900,000 households, which would need to prove their eligibility. They might cut out nearly 2m households where someone from the age of 75 to 79 lives; or start charging every one of the 4.5m households with someone over the age of 75.

Just to means-test pensioners for their eligibility for free licences raises civil liberties issues. The Department for Work and Pensions would almost certainly have to open up its records to allow BBC officials to access private information on the finances of the over-75s. It would cost £72m simply to administer the system.

But there are other very good reasons why the pensioners’ free TV licence should not be abolished. A policy of “taxation without representation” sparked the US war of independence in the 1770s. Since then the convention has been that taxation can be imposed only by the elected representatives of the people.

But if the BBC – an unelected body – becomes the taxing authority, it will decide who is to be taxed for the licence fee, and at what rate.

For the BBC to now make judgments that only parliament should make about the distribution of income between social groups is indeed taxation without representation.

The BBC’s argument is that its budgets are stretched to the limit and that it has no alternative but to recoup as much of the £800m that the over-75 concession costs. To make its case, it claims BBC finances have been cut back to the bone. So it’s an irony that a few days ago the BBC’s top brass announced they would award themselves bonuses of up to £75,000 – giving some of them 30% rises in a multi-million pound handout.

But there is a far more fundamental reason why pensioners should not pay. The Frontier Economics report – commissioned by the BBC to make its case – does not even acknowledge that pensioner poverty, which was halved between 1997 and 2010, is now on the rise again – from 1.6 million three years ago to 1.9 million now – and forecast to pass 2 million by 2022. In the BBC’s statements, there is a complacency about today’s pensioner poverty that I find distressing and alarming, especially when over‑75s are almost 50% more likely to be in poverty than the 65-75 age group. In fact, one in every four of the over-75s is eligible for pension credit because their income is so low. As the fee rises towards £160, and then £170, that poverty will become worse.

Of course there is a very good reason why the last Labour government and then the Conservatives promised a free licence to all over-75s regardless of income. Support for the welfare state is dependent on us feeling we are “all in this together”: that means combining targeted benefits such as the pension credit (which took 2 million pensioners out of poverty) with universal benefits that cover everyone. The free TV licence Labour introduced in 1999 is one of the few universal benefits available to all very elderly pensioners, and is particularly important given that for millions who live on their own the television is the best antidote to loneliness and isolation.

Backed by an Age UK petition, Tom Watson, Labour’s culture spokesman, has made the case that if the BBC needs extra money, the government itself – not the broadcaster – should take responsibility for finding it. To do so is the only fair way of keeping its election promise.

• Gordon Brown is the UN special envoy for global education and a former prime minister of the UK

The Age UK petition can be signed here