He also lambasted the management competence of another colleague, Mike Killian, head of the Tokyo office, who has escaped criticism in the inquiries so far.
Mr Baker told the Commons Treasury Committee inquiry into Barings that his ability to discharge his responsibility was "greatly inhibited by what, under any reasonable interpretation of the known facts and events, was a cover-up, commencing around mid-January 1995''.
Mr Baker, a director of Baring Brothers who took formal responsibility for Leeson's securities department on 1 January 1995, six weeks before the crash, said he had inherited organisational chaos from the previous management of the operation.
He told the MPs that the cover-up related to a suspected pounds 50m fraud at Baring Futures (Singapore) and culminated on 2 February 1995 with the "fraudulent use of my name and office, to obtain audit clearance from Coopers & Lybrand Singapore for a spurious transaction invented by Nick Leeson to cover his cash flow deficit in account 88888 at the year end 1994." The fraud was part of the pounds 900m collapse of Barings.
The 88888 account was a key tool in Leeson's fraud. Mr Baker said the use of his own name for this purpose "appears to have been known about by Simon Jones, the chief operating officer of Baring Securities Asia, and in my opinion, was also known about by James Bax." Mr Bax was another senior Barings executive.
"If they now claim they did not know about the use of my name, then on what basis did they subsequently believe Coopers & Lybrand Singapore provided them with the audit clearance for Baring Futures (Singapore), which they sought and obtained in London for Barings plc on 3 February 1995?"
Had Mr Bax suspected this fraudulent authorisation of an apparently bone fide transaction to be genuine then he was certain he "would have, or should have, questioned me about it at the time. As it was, Peter Norris, a senior executive, subsequently described the transaction on 8 February 1995 as an operational error which would be investigated by James Bax. Contemporaneous authorisation of an operational error is simply not possible, by definition."
Mr Baker also fiercely criticised Mr Killian, head of Baring Securities in Tokyo, for losing interest in his job, becoming cynical about Barings and then moving his base to Portland, Oregon.
He said "by acting as he did he had effectively given up the right to manage the business in Asia." He denied the two had been involved in a power battle that Mr Killian had lost but conceded that there was "a difference of opinion about how the business should be managed".
Mr Baker told the MPs he had six weeks to uncover the Leeson problem, "from a situation of inherited organisational chaos and where Barings senior management, either knowingly or unknowingly, conspired with the fraudster to cover things up from Simex [the Singapore Monetary Exchange], the auditors and FPG [financial products group] and me."
Mr Baker's forthright defence of his own actions and his attack on his colleagues in Barings contrasted dramatically with the consistent refusal of other Barings figures, including Peter Baring, the chairman, to name names or throw mud when interviewed by the select committee Mr Baker's criticisms were much closer to the analysis of the Singapore report into Barings than that of the Bank of England.
Geoffrey Barnett, Barings' chief operating officer, refused to make any personal criticisms when he spoke yesterday just before Mr Baker.