Campaign to oust Prime Minister gathers pace

Labour rebels launch coup attempt against Brown on eve of crucial elections. Blears becomes focus of opposition after dramatic resignation from Cabinet

Gordon Brown was clinging on to his job last night as rebel Labour backbenchers threatened to force him out of Downing Street within days.

The Prime Minister suffered a crushing blow when Hazel Blears resigned as Communities Secretary on the eve of local and European elections today that could seal his fate. Ms Blears was incensed by Mr Brown's description of her non-payment of capital gains tax on the sale of two London flats as "totally unacceptable".

Her timing was devastating, and seen as a deliberate attempt to destabilise Mr Brown and trigger a coup. It was the fourth ministerial exit in 24 hours and the second from the Cabinet.

Mr Brown faces a twin threat: a round-robin email circulating among Labour MPs calling on him to step down in the interests of the party and the nation, and a difficult cabinet reshuffle which could backfire rather than end the chaos engulfing his Government.

Organisers of the "Brown must go" campaign claimed that 80 backbenchers may be ready to sign the email. They intend to go public on Monday if they get at least 50 backers.

Another option being discussed is securing the 70 names needed for a "stalking horse" candidate, possibly a left-winger such as John McDonnell, to stand for the leadership. Such a huge revolt could force Mr Brown to quit without a special conference being called. That would open the way for other cabinet ministers to enter the leadership race. "We will get there, one way or the other," one Labour MP predicted last night. "It's tragic, but Gordon is not up to it. The only way to get out of this mess is to have the leadership contest we needed in 2007 [when Tony Blair resigned] or last year."

There were growing signs that ministers may scupper the smooth reshuffle Mr Brown desperately needs to restore his battered authority. Alistair Darling made clear he will leave the Cabinet if he is ousted as Chancellor, dashing hopes among Brownites that he would succeed the departing Jacqui Smith as Home Secretary.

David Miliband, another possible candidate for the Home Office, wants to remain as Foreign Secretary, while the Health Secretary Alan Johnson, the man most likely to take over if Mr Brown is ousted, is also reluctant to move to the Home Office.

John Reid, the former Home Secretary and a Blairite, turned down the offer of a surprise cabinet comeback in private talks with Mr Brown. The Independent understands that Mr Reid stopped Mr Brown in his tracks before a specific job was mentioned.

There was speculation that Mr Reid was offered a return to the Home Office. Brown aides insisted they had merely talked about football. Mr Reid is chairman of Celtic FC.

Amid a feverish atmosphere at Westminster, there were even remarkable rumours that the Prime Minister would offer a post to Mr Blair. Mr Brown is keen to recruit a Blairite "big beast" to dissuade allies of Mr Blair from joining the revolt against him – as he achieved last October by recalling Lord Mandelson, his long-time foe.

The Business Secretary, who rallied strongly behind Mr Brown yesterday, will be a pivotal figure in the critical 48 hours ahead. Blairite ministers such as James Purnell and John Hutton are likely to seek Lord Mandelson's advice on whether they should stay in the Cabinet. If any of them refused to serve under Mr Brown, it could bring him down. But there was no sign of that yesterday, when several ministers including Mr Johnson rushed to the Prime Minister's defence in a frantic round of media interviews.

Some backbenchers and ministers will make a final decision on whether to back or try to sack Mr Brown after the council results emerge tomorrow and the European Parliament results are announced on Sunday night.

One cabinet minister said: "If we come fourth behind Ukip in the Euro elections, that could be the trigger."

Mr Brown and his advisers will decide today whether to bring forward the reshuffle from Monday to tomorrow in an attempt to end the disarray sparked by the departures of Ms Smith and Ms Blears.

Allies insisted Mr Brown would not be pushed out and were relieved that he was not outgunned by David Cameron at Prime Minister's Questions. They dismissed the idea that ministers were threatening to scupper the reshuffle, saying that manoeuvring for jobs always happens before such a shake-up.

Brown allies warned rebel backbenchers that installing a new leader would make the growing demands for an early general election unstoppable, and pointed out that many of his Labour critics would lose their seats.

Barry Sheerman, a normally loyal senior Labour backbencher, said: "If the Prime Minister doesn't realise that, across the party, there is a disillusionment with the way the parliamentary party has been consulted, treated and valued, he is heading for trouble."