The corridors of power ...

Although the prime minister was aware Mandelson’s departure would create shock waves, he assumed it would be quickly forgotten. He was wrong.

Blair has already grossly misjudged the ‘value’ of the Dome. He saw it, three years ago, as a springboard from which Labour could launch their 2001 election campaign.

In fact it haunts him as a monument to incompetence and mismanagement.

So the spectre of Mandelson will remain, not simply to bedevil Blair, but to remind voters of unorthodox conduct at the heart of government.

Mandelson may be politically dead, but he is not lying down. To the fury of the prime minister, he is not going quietly, but has engaged lawyers to fight for his honour.

If Mandelson wants revenge on Blair who sacked him and press secretary Alastair Campbell, who helped, his task is not difficult.

By all accounts, Mandelson was booted out after a 45-minute spat with little opportunity to defend himself. Once the Blair/Campbell axis had decided he had to go, there was nothing else to say.

The affair also resurrected other embarrassments: notably the #1m donation by Bernie Ecclestone, prompting the government to exempt Formula One racing from the tobacco sponsorship ban.

It was no coincidence that Mandelson was depicted as a snake in the TV show Spitting Image. He will hiss and strike until he can clear his name.

The extent to which the government is panicking about this is demonstrated by the condemnation of Mandelson by a succession of ministers.

It resembles the way the shadow cabinet orchestrated its condemnation of Ann Widdecombe over her remark about dealing with drug users.

Blair is now slowly coming to appreciate how dangerous Mandelson may become. The whole affair could cost Labour scores of seats.

• Chris Moncrieff is a senior political analyst at PA News.