One of Allen Stanford's own lawyers has emerged as the key figure who prompted regulators to start legal action over alleged $9.2 billion fraud against the flamboyant Texan billionaire who sponsored a $1 million-a-man cricket match.

The US Securities and Exchange Commission lodged a civil suit against Mr Stanford and his Stanford Financial Group last night, claiming that it was investigating "a fraud of shocking magnitude that has spread its tentacles round the world".

The news is a stunning blow for the England and Wales Cricket Board and its chairman, Giles Clarke, who signed a controversial, five-year sponsorship deal worth $100 million (about £70.2 million) with Mr Stanford in a glitzy ceremony at Lord’s last summer.

The SEC's inquiry into the improbably high rates of return on Mr Stanford's investment products had been running since last July, but according to Bloomberg news agency the turning point came last week, when a lawyer for Stanford International Bank (SIB) in Antigua informed the SEC that he wanted to withdraw all the evidence he had given so far.

The attorney's withdrawal is a massive red flag that screams fraud," said Peter Henning, who teaches criminal and securities law at Wayne State University in Detroit.

"If the SEC hadn't turned up the heat by that point, it did then."

Bloomberg said that a source familiar with the case named the lawyer as Thomas Sjoblom , of Proskauer Rose LLP. Mr Sjoblom is an expert in financial fraud who previously spent 20 years working for the SEC before joining Proskauer Rose in 1999.

He has refused to comment, and Brian Bertsch, Mr Stanford's spokesman, was last night referring all questions about the case to the SEC. Mr Stanford has denied any wrongdoing.

Last night, as investors arrived in Antigua to rap on the door of SIB demanding to know the whereabouts of at least $8bn, Mr Stanford’s own whereabouts were not immediately known. A dual US-Antiguan citizen, he reportedly spends fewer than 90 days a year in the United States for tax purposes, and has a number of homes from Antigua to St Croix in the US Virgin Islands and Miami. He was given a Commonwealth knighthood by Antigua.

Details were emerging today of how he has courted US Congressmen with donations and trips to the Caribbean, in an apparent attempt to minimise his tax liabilities. He has also been photographed with President Obama.

Yesterday a judge in Detroit froze Mr Stanford’s estimated $2.2 billion fortune, as well as the assets of two other top executives, and US marshals raided the Houston headquarters and offices in Memphis and Tupelo of the privately-owned parent company, Stanford Financial Group, which says it manages more than $50 billion in assets.

Bank regulators in Panama meanwhile said they had taken over Stanford Bank (Panama) after anxious investors launched a run on the bank.