Former BP boss John Browne calls on companies to disclose number of LGBT staff they employ

According to the latest Female FTSE Board Report from Cranfield School of Management, the percentage of women on boards in the UK's 100 top companies has increased to 20 per cent.

“That’s after 40 years,” he said. “We’ve come a long way but it shows how much effort is needed to change attitudes.”

When it comes to the number of openly lesbian, gay or bisexual business leaders “we’re probably at year 10 in terms of progress,” he said.

However, the “parallels” between gender and LGBT eventually break down because a woman joins the workplace under no guise and there is a business objective to help her move upwards.

“Now let’s take a man who is openly gay at university; he goes straight back into the closet in the workforce and until he feels that he can say what his sexuality is, he will keep it to himself. That’s the difference.”

Apple chief executive Tim Cook only recently publicly acknowledged his sexuality and remains in the minority of FTSE 500 chief executives (CEOs) to do so. Browne said Cook’s decision to disclose is among one of the most important he could have done to foster an environment of inclusion and signal that success is possible regardless of sexual inclination.

The business case for an inclusive organisation was made in a recent survey of senior LGBT business figures by networking organisation OUTstanding. Of the 200 people polled, 85 per cent thought closeted workers spent too much energy on pretending to be straight and 61 per cent said as a result, they will not work as hard for their company.

Before any headway can be made in turning this around, company CEOs have to set the right tone for the business.

“All it needs is a few CEOs nudging and pushing to make a difference,” he said. And whilst many leaders are yet to pave a way by opening up personally, LGBT networks within organisations have been widely supported and encouraged.

“These are fine but they’re nothing like enough. Unless they have straight allies on them and are connected to the top then they are interesting places to swap stories but they don’t actually communicate and affect the company,” he said.

“And seeing as we know almost all CEOs are straight, the CEO downwards has to be connected as well as through people who joined an LGBT network because they are gay. So it’s not enough to say the LGBT folk will look after themselves on this one. They won’t.”

Browne went on to call for businesses to invest more time and resource into measurement. He suggested employees, including those at executive level and on the board, are voluntarily asked to state their sexuality.

“And companies would be required to report on it,” he said.

For global businesses operating in countries where homosexuality remains illegal Browne said there are numerous challenges but ensuring suppliers have the same policies about LGBT inclusion before working with them is a small step in the right direction.

Finally, in the light of the many industries fearing a talent shortage, CEOs ignore these issues at the risk of being overlooked by young people joining the workforce.

“People who had to reconcile contradictions early in their life tend to think a lot, tend to be on point. And to send signals that [LGBT employees] are doomed [to climb the ladder] – why would they bother joining?”

Commenting on what can be done in marketing and advertising, Sorrell said many clients remain wary of being "offensive" by showing gay couples in campaigns.

"We had one client recently where we had the option to include a gay couple and it was rejected for being too provocative," he revealed.

However, brands such as Tiffany &Co and Coca-Cola have featured same-sex couples in their advertising.