HBOS is preparing to hand the Financial Services Authority its own detailed account of last week’s unusual trading patterns in the bank’s shares to aid the UK watchdog’s investigation into possible stock manipulation.

Shares in the UK bank plunged as much as 17 per cent last Wednesday when false rumours spread that it had sought emergency funding from the Bank of England. HBOS and the UK central bank categorically denied the rumours and the FSA launched an inquiry into potential market manipulation.

HBOS has been piecing together its comprehensive version of the share price movements to help uncover what caused the mass sell-off of its stock.

Its report is expected to provide information on the nature of the rumours that triggered the share price fall, where they came from and a breakdown of when they occurred.

HBOS is understood to have approached Richard Wyatt, the experienced stockbroker, to help uncover any possible rogue trades. Mr Wyatt founded Schroders Securities and Panmure Capital and has been in the industry for 25 years.

FSA officials are on Tuesday expected to receive the full details of the millions of trades carried out last Wednesday. The watchdog will conduct an “exhaustive” analysis of HBOS trades to unearth any that could give cause for concern.

“The FSA is in the driving seat, but we are trying to help them,” HBOS said Monday. “It is important that the culprits are caught. What happened last week was very serious indeed, not just for our stock but for the banking system in general.”

Shares in HBOS have rebounded fairly quickly. On Thursday, 250 of the bank’s senior managers and a number of non-executives bought a total of £6m worth of shares, which helped restore confidence.

The FSA is also due Wednesday to release a report into the collapse of Northern Rock, the UK mortgage lender that was nationalised earlier this year.