An email which Herve Falciani, the whistleblower at the centre of the HSBC tax row, says that he sent to HM Revenue and Customs in 2008 has been uncovered by a French newspaper.
HMRC said it had no record of the email.
But Mr Falciani said he had offered it information on clients from one of the five biggest private banks “in the world” that is “based in Switzerland”.
Le Monde has since uncovered the email and shown it to the BBC.
Mr Falciani said he felt vindicated: “It required seven years of battles to get the point we are just now.”
Speaking to BBC business editor Kamal Ahmed, he added: “It proved that I’m right.”
During Wednesday’s parliamentary committee hearing, Lin Homer, head of HMRC, was questioned forcefully over whether the tax authorities had received a communication regarding HSBC’s tax arrangements.
Ms Homer said she had “no knowledge” of an email in 2008.
A spokesperson from HM Revenue and Customs said on Thursday: “HMRC has not found a record of receiving an email or any phone call from Mr Falciani in 2008.
“As Lin Homer said at the PAC, we are looking into whether HMRC received an email or phone call, and if we did, what then happened.”
Mr Falciani said he thought HSBC should be prosecuted and that many other banks could be drawn into the matter.
HSBC says it has already reformed its practices.