Four law firms have been included in this year's Workplace Equality Index compiled by gay rights charity Stonewall.

The index, which ranks the top 100 gay-friendly employers in the UK, included Simmons & Simmons as the highest-ranked law firm in 15th place, up from 31st place last year.

Elsewhere, Pinsent Masons ranks 36th, up from 50 in 2009, Herbert Smith moves from 77th to 56th position and Eversheds has risen to 85th up from 100 last year.

In total, 24 law firms submitted entries to Stonewall this year.

Computing giant IBM topped the rankings for the second time in four years, replacing last year's winner Lloyds TSB.

The process sees companies nominate themselves to participate through an online survey giving evidence of their policies. An anonymous staff survey is then carried out, which this year saw 7,000 lesbian, gay and bisexual participants. The top 20 finalists are then separately audited.

Stonewall chief executive Ben Summerskill said: "We received more entries than any previous year from employers who understand and have benefited from Stonewall's research which found that gay people are far more likely to buy goods or services from companies they know are gay-friendly."