The boss of pharmacy giant Boots was accused yesterday of lining his own pockets with millions of pounds at the expense of British taxpayers.

As the retailer's parent company opened its convention in Monaco, charity War on Want said it had new evidence regarding £400 million in transactions made by organisations related to the firm.

These deals appear to have enriched Alliance Boots executive chairman Stefano Pessina at the expense of both the company and the British public, the charity said.

Research conducted by War on Want and the US trade union federation Change to Win has triggered a complaint with the Organisation for Economic Co-operation and Development (OECD).

It is alleged that Alliance Boots violated the OECD Guidelines for Multinational Enterprises by inadequate disclosure of insider transactions and avoidance of tax.

The firm is believed to have dodged tax by paying out interest to related entities rather than treating those payouts as taxable dividends.

The complaint details how two Irish subsidiaries of a Luxembourg-based finance company - apparently controlled by Mr Pessina - bought more than £220m of Alliance Boots' debt.

These subsidiaries then funded the purchase of the debt by issuing "profit participating notes" which were bought by Alliance Boots itself.

Debt was sold back to Alliance Boots this year at what is believed to be a handsome profit, retaining the majority of the returns generated by significant appreciation in the market value of the debt.

The 2007 buyout was funded with more than £9 billion of debt, enabling massive interest deductions in Britain that allowed the company to avoid more than £1bn in corporation tax.

The debt used to finance this deal was packaged and securitised as collateralised debt obligations, which were sold by banks to private investors.

War on Want executive director John Hilary said: "These transactions demonstrate a failure of corporate governance and abuse of the tax system that is unconscionable from one of Britain's largest corporations."

The allegations appear at a time when corporate disclosure and tax avoidance are coming under increased debate and government scrutiny.

Peers recently called for large companies to disclose their tax returns publicly and implement strong corporate governance regimes to "help to curb tax avoidance and other destructive practices."