The England and Wales Cricket Board and the Professional Cricketers' Association sent a letter to Butt on behalf of the team, seeking “a full and unreserved apology.” “Mr. Butt has been advised that if a satisfactory response is not received, legal proceedings will be commenced against him without further notice,” the ECB said in a statement.

England's players were outraged after Butt accused the team of throwing Friday's one-dayer at The Oval, which Pakistan won after an England late-order collapse to keep the five-match series alive at 2-1.

Butt's allegations came after an investigation was opened by the International Cricket Council following claims the scoring in Pakistan's innings on Friday was prearranged.

It was the latest incident to mar Pakistan's scandal-filled tour, which ended on Wednesday when England won the fifth and deciding one-dayer at the Rose Bowl in Southampton by 121 runs to claim the series 3-2.

The tour has been mired in controversy ever since three players - Salman Butt, Mohammad Asif and Mohammad Amir - were accused of spot-fixing allegations in the fourth test at Lord's last month.

The trio was alleged in a newspaper sting to have ensured deliberate no-balls were bowled to order to facilitate a gambling syndicate. The players maintain their innocence but were charged and suspended under the ICC's anti-corruption code.

A fourth player, Wahab Riaz, was also questioned by police under caution before being unconditionally released.

Tensions between the two teams reached a low point on Monday when England captain Andrew Strauss said his team had had mixed feelings about taking to the field for the fourth one-dayer at Lord's.

Strauss said he and his teammates were disappointed their integrity as cricketers had been questioned by Butt, and vowed to “explore every possible avenue” to clear their names.

Butt, who claimed he heard rumors from bookmakers that England players had taken “enormous amounts of money” to lose the third one-dayer, was adamant there was a “sinister conspiracy” against Pakistan cricket.

The Pakistan squad will return home having lost the test, Twenty20 and one-day series to England.