The ECB and the Professional Cricketers' Association have sent a pre-action letter to PCB chairman, Ijaz Butt, seeking a "full and unreserved apology" for alleging that England's players were involved in fixing the outcome of the third ODI at The Oval, which Pakistan won by 23 runs.
The letter, sent on behalf of the England team, advised Butt that "if a satisfactory response was not received, legal proceedings will be commenced against him without further notice."
The Pakistan board said it had instructed London lawyers, Addleshaw Goddard, to respond on its behalf to the ECB's letter.
"The PCB confirms that it has received a letter from English solicitors acting for those who represented England in the one-day international last Friday 17th September, in connection with statements said to have been made to the media by Mr Ijaz Butt, chairman PCB," the board's release said. "In this letter multiple demands have been raised."
In an extraordinary statement last Sunday, which he read out to ESPNcricinfo, Butt had said, "There is loud and clear talk in bookie circles that some English players have taken enormous amounts of money to lose the match [the third ODI]. No wonder there was such a collapse." He had also accused certain "august cricket bodies" of conspiring to defraud Pakistan and Pakistan cricket.
The allegations were made after the ICC announced it was investigating the third ODI at The Oval after receiving information from a newspaper before the game began alleging that bookies were aware of certain scoring patterns that occurred during the match.
"We are looking for an apology. If it does not come we'll look at other options," ECB chief executive, David Collier, had said on Tuesday. "You can't impugn someone's integrity without having proper evidence. "To date I can say that we have received zero evidence of anything having influenced any England player."
Andrew Strauss, the England captain, had said his team was outraged by the allegations Butt had made. "We are deeply concerned and disappointed that our integrity as cricketers has been brought into question. We refute these allegations completely and will be working closely with the ECB to explore all legal options open to us."