Mr Hague had agreed at 11 o'clock on Monday night, over drinks in Mr Howard's grace and favour flat in Belgravia, that he would be the deputy leader and chairman of the party, giving Mr Howard an unstoppable run at the leadership.
The celebratory drinks were shared with Mr Howard's wife, Sandra, Mr Hague's girlfriend, Ffion Jenkins, 28, and Sir Michael Spicer, Mr Howard's campaign manager.
But the champagne feeling turned flat at 8am yesterday when Mr Hague, 36, rang the former Home Secretary to tell him that, having slept on the idea, he had second thoughts - he was running for the leadership, and the deal was off.
Mr Howard was furious, but put a brave face on it yesterday, as he announced his intention to run for the leadership without Mr Hague's support.
After confirming Mr Hague had had second thoughts, Mr Howard said he did not rule out Mr Hague joining his shadow Cabinet if he was elected leader.
"I have the highest opinion of Mr Hague," he said. "I certainly intend that he should play a part in the team."
He added that there could also be places for two of his declared rivals for the job - Kenneth Clarke and John Redwood, who also launched his campaign yesterday
Mr Howard said that it would be "silly" to pretend that he and Mr Clarke agreed on everything but he said they had been friends for 37 years and there were a large number of issues on which they were agreed.
The champagne supper, like a party that got out of hand, left both camps with a bad hangover, and embarrassment on all sides. The opposing Lilley and Redwood camps could not hide their glee at the set-back for both Mr Howard and Mr Hague. "It just shows that they still couldn't organise a p***-up if they tried," said one Redwood campaign supporter.
There had been intensive talks over the telephone for the past three days, about Mr Hague throwing his support behind Mr Howard.
"It was agreed over the telephone that William would be the deputy leader and chairman of the party. They were really only agreeing the details of the campaign. The meeting lasted about an hour and they broke out the champagne to celebrate. It was obviously a winning ticket.
"William rang Michael early this morning to say it was off," said one of Mr Howard's supporters. "The whole thing is unfortunate."
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