Barclays' finance director has called for an overhaul of opaque and complex accounting rules that artificially boosted the profits of big European and U.S. banks by billions of pounds in the third quarter of this year.

In a letter published in Monday's Financial Times, Chris Lucas said the requirement for banks to adjust their figures to reflect the market value of their own debt was widely believed to distort their actual profits.

It makes results difficult to explain to investors and is unhelpful for an industry that wants to rebuild confidence through transparency in financial reporting, he wrote.

The FT said so-called fair value accounting of own debt means banks adjust their earnings to reflect the current price at which they could buy back their own debt in the market.

If their debt is viewed as riskier, meaning there is a higher chance of default, it is worth less, so banks could in theory buy it back more cheaply.

This means that in difficult market conditions, such as those in recent months, banks are able to book large artificial gains in their financial results, according to the article.

(Reporting by Stephen Mangan; Editing by Matt Driskill)