One of the largest professional services firms in the world, Ernst & Young, has topped Stonewall’s list of the 100 best employers for gay and bi employees this year.

Among 25 new entries for 2012 is MI5, the UK’s counter-intelligence and security agency, at number 62.

Until 1989, the agency saw gays as too “vulnerable to corruption” to perform the high-level work at Thames House, but the Security Service now has a popular support group for LGBT employees.

Ernst & Young tops the Top 100 Employers 2012 list, up from third place last year.

The Home Office has been knocked off the top spot to second place, and Barclays has risen from tenth place to occupy third.

Stonewall says the 2012 Index has been revised with the most demanding criteria to date, introducing new weighting for global employers that recognises worldwide support for LGB equality.

The Employee Network Group of the Year goes to Accenture, and the Department of Energy and Climate Change is named Most Improved Employer.

Bill Payne, former Chief Executive of Metropolitan Housing Partnership, was named Individual Champion of the Year.

The full results will be announced at a ceremony tonight, hosted in London by Ernst & Young.

Lynne Featherstone, MP, Minister for Equalities, will present the accountancy firm with their award for Top Employer.

Liz Bingham, the firm’s Managing Partner for People said the commitment to diversity was important for employees, and “a business imperative in what is an increasingly competitive and interconnected world”.

Ben Summerskill, Stonewall Chief Executive said: “Competition for a place in the Top 100 was fiercer than ever this year.

“With new, more demanding criteria, every employer securing a position in the Top 100 has performed impressively – and the participating employers collectively employ over 1.9 million people.

“The Index remains a powerful tool used by Britain’s 1.7 million gay employees and 150,000 gay university students to decide where to take their talent and skills.”

Jonathan Evans, Director General of MI5, said: “The Security Service has worked hard in recent years to promote equality and diversity across all areas of its work. We are pleased to be recognised by Stonewall, but there is still more we can do. We will continue to support lesbian, gay and bisexual staff to make MI5 a truly inclusive place to work.”

The Index is based on a range of key indicators which this year included a confidential survey of lesbian, gay and bisexual employees, with over 7,500 participants.

This consistently confirmed that the satisfaction levels of gay staff were highest at the top-ranking organisations in the Index.

The top ten employers have been revealed as:

1 Ernst & Young
2 Home Office
3 Barclays
4 Sussex Partnership NHS Foundation Trust
5 Metropolitan Housing Partnership
6 Goldman Sachs
7 Accenture
8 IBM
9 Gentoo
10 Simmons & Simmons