It takes a steady hand and delicate skill to push a wire safely into a human heart. Although Downing Street had described the procedure on Blair’s heart “flutter” as routine, only some 60 doctors in Britain have the skills to carry out a technique that has been perfected only in the past 10 years.

If such thoughts crossed Blair’s mind, at least he knew that in Lefroy and Davies he had the best experts on offer.

They slid a tiny probe — a catheter — into a blood vessel in Blair’s leg. Then Davies, an expert from St Mary’s hospital in Paddington who had been summoned for the task, manoeuvred it with painstaking care upwards into Blair’s chest and the wall of his heart.

Once there they had to locate the source of the electrical malfunctions that were causing Blair’s heart at times to beat at twice the normal rate. It was said to be an area about two millimetres wide.

After about two hours the procedure was complete and appeared to have been successful. Doctors had predicted that Blair would spend a night or two in hospital to recover. But this is a prime minister with a point to prove: that he was no lame duck leader, no invalid clinging to power.

At 2.55pm Blair was on the phone to Hilary Armstrong, his chief whip. By evening he was back in Downing Street, although ordered to rest.

His heart was back beating normally. He was ready to go on as prime minister, and on. True, it had emerged that he and his wife Cherie had quietly bought a £3.6m London house for the day when they leave Downing Street; but that was just prudent preparation, the spinners said.

The day before his surgery Blair had declared that he would serve a full third term if Labour won another general election. Then, with either extraordinary frankness or hubris, he added that he would not seek a fourth term.

No other prime minister had laid out his ambitions and limitations so starkly. No other leader has set his departure date years in advance.

Was it a snub to Gordon Brown, who has so long coveted the job? Had Blair performed a triple-bypass on Brown’s chances of ever becoming prime minister? “This completely screws Gordon,” said one Downing Street aide.

Others suggested the exact opposite: that Blair had at last made it clear when Brown might take over, and his decision to go at the end of a third term would calm the feverish speculation over Labour’s leadership.

Yesterday that hope seemed misplaced. While some allies of Brown remained cool about Blair’s ambitions, others barely concealed their anger.

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