Gillian Duffy, the Rochdale pensioner whom Gordon Brown described as "a sort of bigoted woman", turned down the chance to make a small fortune from selling her story to The Sun because the newspaper wanted her to say things she did not believe.

The offer was made during a classic newspaper attempt at a "buy up", conducted in cloak-and-dagger style only hours after Mrs Duffy's chance encounter with the Prime Minister had made her a media star.

After Gordon Brown had emerged from a 39-minute meeting in Mrs Duffy's home to announce that he was a "penitent sinner" and that she had accepted his apology, about 50 newspaper and broadcast journalists, photographers and camera crews spent the rest of the afternoon and evening camped outside Mrs Duffy's white PVC front door, hoping that she would come out to speak to them.

It could have been a long, dull wait for them all, because the only action at the front of the house was a brief appearance by John Butters, of the public relations firm Bell Pottinger, who told them that Mrs Duffy would not be saying anything else that evening.

What they almost missed was the action round the back, where an intrepid Sun reporter, Richard Moriarty, and a photographer, Jimmy Clark, were clambering across hedge and fence in failing light to sneak in through the back garden, unseen by their commercial rivals.

But newspaper offices are leaky places, and it was not long before word was going around the London headquarters of rival papers that The Sun was up to something. Reporters waiting at Mrs Duffy's doorstep started receiving calls from the office asking whether they could see anything happening inside the house. The answer was "no". The next question was: "Where are the men from The Sun?"

The answer was that the Sun contingent was nowhere to be seen, but it took only an instant for the media pack to guess what was afoot, and, with a clatter of hastily gathered-up cameras, they raced to the back of the house, just in time to see a flash of light coming from a kitchen window which told them someone inside was taking photographs. The kitchen curtains were drawn before they could see anything more.

But around 8pm, Moriarty rejoined his colleagues. According to one, he looked "sheepish". The deal with The Sun had fallen through. As darkness fell, most of the media pack dispersed, although two Sunday newspapers maintained a vigil outside Mrs Duffy's door. Around 7am yesterday, the pack was back outside her door – though they numbered only about 20, rather than the 50 who had been on duty the previous day. That was enough to make Mrs Duffy want to escape. At 8.15am, a man drove up to her house in a grey BMW and whisked her away.

But a hungry pack of journalists is not easily shaken off. Someone established that the BMW belonged to Mrs Duffy's daughter's partner. A scout was sent to her daughter's house in another part of Rochdale. He rang to say he had spotted the BMW, and the pack moved to maintain the siege outside a different door, where two community police officers stood guard. Mrs Duffy spent the day indoors, with curtains drawn. Soon after lunch, Mr Butters went in, but emerged later to announce that Mrs Duffy was still not saying anything.

There was speculation yesterday that The Sun had offered Mrs Duffy £50,000, or even £75,000 for her story. It is more probable that The Sun's offer was in the range of £25,000 to £30,000 – which must still have sounded like riches to a pensioner who has worked all her life on relatively modest wages. But Mrs Duffy turned it down. Reputedly, The Sun, which has been campaigning aggressively since last October for a Conservative victory, wanted her to attack Gordon Brown in unrestrained language and declare her support for David Cameron but, after a lifetime's allegiance to the Labour Party, she would not do it.

Another rumour is that Andy Coulson, the former News of the World editor who is David Cameron's link with the Murdoch empire, contacted Rebekah Brooks, chief executive of Murdoch's company, News International, to say that it would not help the Tory cause if The Sun pushed its suit too hard. Coulson's reasoning was that Labour was in such a mess after Gordon Brown's gaffe that it would pay to leave them dangling in the wind rather than give them a pretext for claiming that Mrs Duffy was party to a Tory-orchestrated media conspiracy.

Even without the involvement of The Sun, the presence of a man from Bell Pottinger set off conspiracy theories. The agency was founded in 1987 by Tim Bell, Margaret Thatcher's advertising guru, who advised her through the victorious 1979 election campaign. The chairman of Bell Pottinger Public Affairs, Peter Bingle, is a Tory activist who wrote a jubilant blog yesterday, jokily suggesting: "There is a strong case for giving Gillian Duffy a peerage. She has revealed the true Gordon Brown."

This prompted speculation that the Conservatives had deployed Bell Pottinger to persuade Mrs Duffy to cause maximum embarrassment to Mr Brown. A counter-rumour was that another Bell Pottinger director, David Hill, had stepped in. He is an old Labour Party hand, who succeeded Alastair Campbell as director of communications for Tony Blair. It was thought that he may be pulling Mrs Duffy's strings.

The truth is more prosaic. Finding herself under siege from the media, Mrs Duffy rang her daughter, Debbie, seeking help. Her daughter works as head of compliance at the Manchester office of the solicitors' firm DWF. The firm uses Bell Pottinger North to handle its public relations. Debbie contacted John Butters, of Bell Pottinger North, who agreed to help.

"This has got no link to any political associations that Bell Pottinger as a group might have," Mr Butters said. "This comes purely from the family connection. We have not tried to influence Mrs Duffy in any way, we have simply passed on to her the options that have been put to us. These range from doing a deal with a particular newspaper, to just reading out a statement outside the house. There have been lots of offers that have been declined, and some are still on the table."