Lawyers and family of Hayes, a former UBS (>> UBS Group AG) and Citigroup (>> Citigroup Inc) derivatives trader, failed to overturn his conviction in a case closely-watched by the banking industry.

John Thomas, the head of the judiciary in England and Wales, and senior judges Brian Leveson and Elizabeth Gloster said although Hayes had committed serious harm and a "deterrent element was plainly required", they believed the overall sentence was longer than was necessary to punish Hayes and deter others.

"However, this court must make clear to all in the financial and other markets in the City of London that conduct of this type, involving fraudulent manipulation of the markets, will result in severe sentences of considerable length which, depending on the circumstances, may be significantly greater than the present total sentence," they said.

Hayes, 36, was diagnosed with Asperger's syndrome shortly before his 10-week trial began in May. He was sentenced to one of the longest prison terms on record for UK white collar crime after he was found guilty in August of eight counts of conspiracy to defraud.

Prosecutors said the former Tokyo-based trader was a ringleader in a four-year scam with others to fix the London interbank offered rate, that serves as a benchmark for rates on around $450 trillion (£301.7 trillion) of financial contracts worldwide.

In the appeal, the defence argued that High Court Judge Jeremy Cooke made legal errors in the way he handled the case and that the sentence was wrong in principle and excessive.

(Reporting by Simon Jessop; Wrting by Kirstin Ridley; Editing by David Goodman and Jane Merriman)

By Kirstin Ridley and Simon Jessop

Stocks treated in this article : Citigroup Inc, UBS Group AG