According to a report in the Sunday Times, high concentrations of herbicide were discovered in Woolmer's stomach and traces were found inside and outside of a glass from which he had been drinking champagne.

The newspaper also said that the detectives are focusing on two bottles of champagne that were given to him in a gift set. One had been emptied and the other was left untouched in his hotel room.

Woolmer, a 58-year-old former England batsman, died at the Pegasus hotel in Kingston March 18, hours after Pakistan had been knocked out of the World Cup.

The newspaper revealed three weeks ago that forensic tests indicated he had been poisoned.

It has now emerged that the poison was a weed killer so rare that detectives have yet to establish whether it is available in Jamaica.

"Everything was contaminated. The stomach content, the glass, everything. There was enough to kill him," the newspaper quoted a source as saying.

"We think it's something very unusual, that you can't even buy in Jamaica. We don't know what form it was in, whether liquid or crystal. The weed killer was certainly in the glass. We are not sure whether it was in the bottle. Until we get further results we can't confirm it," the source added.

Woolmer proble: Full coverage

If the herbicide was not inside the empty bottle, it leaves open the possibility that the glass was contaminated earlier or that someone may have slipped it in once the champagne had been poured. It is not known whether he shared the bottle of champagne with another person.

Pakistan's former media manager Pervaiz Mir also confirmed that Woolmer had received the champagne.

"I was told that somebody had brought two bottles," he said.

"He told me he was mostly a beer drinker because he was a diabetic and it suited his blood sugar," said Mir.

Toxicologists say there are potentially hundreds of weed killer compounds that could be used as poison. Some have no smell or taste, are soluble in water and can cause an acute reaction within hours.

One expert from Guy's hospital poisons unit in London said such compounds were usually ingested accidentally or by people committing suicide.

"The use of a herbicide in homicide is pretty rare if not totally exclusive to this case," the expert said.

A number of herbicides are commonly used in champagne production. But Tom Stevenson, a champagne expert, said: "The growers are extremely careful and I can't think of any case where even small residues of herbicides or pesticides have been found in a bottle."

Mark Shields, the deputy police commissioner leading the investigation, will this week travel to Britain to meet a team of experts carrying out further toxicology tests and reviewing the post-mortem.