As evidence of a terror bomb campaign, it was both meagre and suspect. On the table at a police press conference lay two pistols with two rounds of ammunition, a knife, loudhailers, cans of spray paint, a clutch of red whistles, opposition party T-shirts and 53 sticks of dynamite with detonators.

These were “similar to those used by the Zimbabwe National Army in demining operations”, police said. No explanation was offered as to how explosives usually kept under strict security in army magazines had found their way to “terrorists” of the opposition Movement for Democratic Change (MDC). Police said that the items were picked up during Wednesday’s swoop on MDC homes and its headquarters in Harare, to seize culprits and equipment allegedly used in nine petrol bombings since March 12.

No one I met yesterday believed the front page of the state propaganda daily, The Herald, announcing the police claims. A contemptuous "aaah" was the usual response. “They [police] were putting those things there themselves,” said Chenga Tsvisvo, an office messenger. But they were central to President Mugabe’s case yesterday at the Dar Es Salaam summit of Southern African leaders.

Mr Mugabe’s case is that the reason for the country’s unfolding crisis is the "orgies of violence unleashed by the MDC with the support of Britain and America to achieve illegal regime change". It has nothing to do with the brutal assault on opposition figures in the past month, the violent trampling on dissent, the curfews, the bans on public meetings and the collapse of the economy, he says.

"That huge operation by the police was organised just so Robert Mugabe could go to Dar es Salaam and have something to persuade his neighbours," said John Makumbe, a political commentator. "The only violence in this country is by the police."

Mr Mugabe’s Government has a reputation as a master of deception of labyrinthine complexity to undermine his opponents. The most renowned was the plot leading to the year-long treason trial of Morgan Tsvangirai, the MDC leader, that started early in 2003, for allegedly trying to recruit international support for Mr Mugabe’s overthrow.

Only well into the trial did it emerge that Ari ben Menashe, a American, had been paid $800,000 (£407,000) by the Government to pose as a “political consultant”, lure Mr Tsvangirai with promises of securing highest-level international lobbying services and entrap him into a fake coup plot, after which he could be hanged.

He was able to draw Mr Tsvangirai to a Toronto office where he was filmed by secret cameras as Mr ben Menashe tried again and again to elicit the words “violent overthrow” from him. Mr Tsvangirai did not oblige, the video and tape quality was so poor that it was rejected by the court and Mr ben Menashe was finally adjudged a charlatan, although he kept the Zimbabwean taxpayers’ $ 800,000.

The most cynical was the case of Cain Nkala, a senior member of Mr Mugabe’s war veteran militia, who was found strangled in a shallow grave outside the western city of Bulawayo in 2001. Earlier, he had been talking to journalists about the direct involvement of Mr Mugabe's Zanu (PF) party in the murder of a local MDC official.

Police arrested six MDC activists and tortured admissions out of them and they were sent to trial with the expectation of being found guilty. That would have given Mr Mugabe the ammunition to declare the MDC a “terrorist organisation” and ban it - and resolve the inconvenient murders of Mr Nkala and the MDC official.

After a two-year trial, the judge dismissed the state case as “surreal,” found that the six had been arrested for murder before Nkala was dead, and that the police investigation records were “an appalling piece of fiction.” The judge also said that the entire affair had been organised by a shadowy state security unit called "the ferret team", made up of intelligence agents, army and police officers and war veterans. The Government was left with the smoking gun that killed Nkala.

This month, The Herald claimed that Christopher Dell, the American Ambassador, had met Mr Tsvangirai at a Harare hotel and handed over a briefcase full of cash. Mr Dell responded that he had been at the Bulawayo museum that day, and said that The Herald could confirm by checking the visitors’ book, if it had not already “torn out the page.”

"They must realise," he said, "that to get the big lie right, they have to get the little lies right."

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