It's untrustworthy, so why do millions of people still buy The Sun?

Why does anyone still buy The Sun? After a week in which it admitted that its reporting of one of Britain's worst disasters was based on a pack of lies, and when a new public poll named the paper as the "least trusted" on the newsstand, it's a hard question to answer. This is a newspaper that remains under intense investigation by Scotland Yard for operating what Deputy Assistant Commissioner Sue Akers, the head of Operation Elveden, has described as a "culture of illegal payments" that funded "a network of corrupted officials". A large chunk of The Sun's news room has been arrested in relation to their alleged involvement in that culture.

This is the sister paper of the News of the World, that nest of phone hacking, which was regarded by its publisher, News International, as such a toxic brand that it had to be closed down. How much more disreputable does The Sun have to be before it is similarly dispatched?

Well, quite a bit, judging by the reading habits of a still sizeable section of the British public. Because on Thursday, when The Sun finally admitted that its reporting of the Hillsborough tragedy was "inaccurate, grossly insensitive and offensive" and to the paper's "eternal discredit", it was also in a position to boast above the masthead that it was "Britain's most popular paper".

Unlike the litany of falsehoods that underpinned its Hillsborough coverage in 1989 (albeit unintentional, it claims), this particular claim was based on fact. Data released by the National Readership Survey last week showed The Sun's monthly combined reach in print and online is a hefty and unrivalled 17,793,000, beating even the Daily Mail and its phenomenally successful Mail Online (16,428,000).

Like The Sun, the Daily Mail is often derided in liberal circles for its supposedly spiteful reporting. But the Mail would say its editorial position merely reflects the values of its army of Middle England readers. It is becoming difficult to see who exactly The Sun speaks for.

The "Currant Bun" used to be a proudly worn badge of identity; propped up on the dashboard of the van, poking out of the back pocket of a pair of jeans or held up on the commuter train by the white-collar reader who wanted to declare an interest in popular culture.

Across the press, and in wider society, it was admired for the wit of its headlines. The Sun was funny and in the know, like a boisterous acquaintance who would occasionally put noses out of joint with a brusque observation but was always good for a laugh.

But the sense that The Sun is no longer regarded so amicably was brought home by a Populus survey last week which identified it as the least reliable title in the British press. Its reporting was trusted by only 9 per cent of respondents.

Things could now get worse. Hillsborough has, for 23 years, been largely a localised sales problem. Costly though the Merseyside boycott has been, The Sun – aided by price advantages funded by Rupert Murdoch's vast global muscle – has maintained its advantage over its great rival, the Daily Mirror. But Thursday's humiliating edition – however sincerely it was produced by the editor, Dominic Mohan – has the potential to damage the brand nationwide.

Of course it was entirely right for The Sun to go down on its knees but, until Thursday, many of its readers up and down the country may have been unaware that the paper had done anything wrong. The apology was "unreserved and heartfelt" but it may have given pause to previously loyal consumers.

Football is integral to The Sun's brand, both on its sports and news pages. Those who died at Hillsborough happened to be Liverpool supporters but a similar fate could have befallen followers of other clubs, who – along with their families – have continued to buy The Sun. They might now consider whether their paper would have subjected them to the same awful treatment.

Indeed, now any central ambiguity over what happened at Hillsborough has been removed, the game of football itself might be more reluctant to engage with The Sun, making life harder for its respected roster of correspondents.

In its defence, The Sun has argued in a contrite editorial that "the vast majority of current employees" were not at the paper in 1989. The News of the World, we may recall, made similar protestations over phone hacking.

Has The Sun changed? Yes, under Mohan's stewardship the paper has lost some of the naked aggression it had during Kelvin MacKenzie's time in the editor's chair. Recently, it clumsily tried to show some of that old shameless bravado by breaking ranks with Fleet Street and publishing naked photos of Prince Harry – drawing widespread criticism rather than any sneaking admiration.

Mohan is trying to make the paper relevant to a younger generation, with heavy helpings of entertainment news and headlines that pun on modern pop songs. These younger readers have probably never stood on the type of caged terraces that contributed to the disaster in Sheffield. The Sun probably felt they wouldn't bear grudges over monochrome pages produced a generation earlier.

The previous doubts about the paper's culpability over Hillsborough were partly down to the obfuscation of MacKenzie himself, and his repeated refusal to acknowledge a gross mistake. He once publicly claimed that the notorious front page "The Truth" was based on material produced by "Liverpool journalists", though we now know it came from the Sheffield-based Whites Press Agency, which clearly had a close rapport with the local South Yorkshire Police.

The Sun has always walked hand in hand with the boys and girls in blue. That relationship has sensationally soured. Rather than helping The Sun, Scotland Yard now has it under investigation. And after years of depending on titbits from police officers – some of whom were so trusted that they were allegedly on the paper's payroll – Britain's biggest tabloid suddenly feels betrayed. "Police Lies 'Disgrace'" was its headline last week as it desperately sought to apportion blame for its own failings. And if The Sun has itself lost confidence in its sources and what it publishes, then why would even those 9 per cent of the public believe what it says any more?