LONDON (Reuters) - Just one of Britain's top 350 companies - RenewablesInfrastructure Group (L:TRIG) - has a "perfect" record on gender diversity, as tracked in a new fund from Legal & General Investment Management.

The L&G Future World Gender in Leadership UK Index Fund, or GIRL fund, is the first such fund to focus on British firms and tilts its relative holdings of each company based on how it performs on four measures of gender diversity.

Companies are graded based on the degree of female representation on the board, among the executive body, in management as well as the broader workforce, factors LGIM is pushing companies it invests in to address.

Under the system devised by LGIM, each company is given a score between zero and 100 on each of the measures, with their combined score determining where they sit in the total ranking.

The target for each measure is 30 percent. Any company with less than that loses marks while any above that gains marks up to a target of 50 percent, which equates to a maximum score and is something only Renewables Infrastructure has so far attained.

Rounding out the 10 best-performing companies are Merlin Entertainments (L:MERL), Ascential (L:ASCL), N. Brown (L:BWNG), Next (L:NXT), Marks & Spencer (L:MKS), UBM (L:UBM), ASOS (L:ASOS), Shaftesbury (L:SHB) and Halfords (L:HFD), LGIM said.

"There's a growing body of evidence that helps support the notion that more diverse leadership teams and boards make better decisions and have higher long-term performance," LGIM Chief Executive Mark Zinkula said.

LGIM and others, including AXA Investment Managers, have said they will vote against the board of companies that perform poorly, backed by data that shows those with more female leaders perform better.

A British government-backed report has set a target for women to make up at least a third of the board at each of Britain's biggest companies by 2020.

LGIM, the third biggest investor in the FTSE 350 (FTLC), said it would launch the fund with 50 million pounds of its own money and make it available to both retail and institutional investors.