Number one sportswear firm Nike has won top marks on an index which rates how 'gay-friendly' companies are.

The Human Rights Campaign's (HRC) rating of 446 firms was based on analysis of company polices including benefits for same-sex partners as well as diversity training for staff.

137 of the other companies in the study also received top marks.

In fact, the number of businesses to get a 100% rating has risen tenfold since surveys began in 2002, when just 13 companies got a top score.

"More companies than ever sought and achieved a perfect score", said the HRC.

"To maintain a perfect rating in 2006 (or, in some cases, obtain a rating for the first time), America's largest corporations are instituting significantly more comprehensive workplace policies for gay, lesbian, bisexual and transgender employees.

"In all of the policy and benefits areas that were measured, this report reveals double-digit increases in the number of companies adhering to the criteria."