ACAS Guidelines make it clear that where an employee's sexual orientation is made public without his consent that this can amount to harassment. I noticed an interesting case dealing with this issue which has just been reported - Grant v Land Registry  EWCA Civ 769 - with the Court of Appeal finding that, in the particular circumstances of the case, such an act was not harassment.
Mr Grant worked for the Land Registry and was openly gay. When he moved office he chose to keep his sexuality private. Unfortunately one of his former colleagues told his new manager that Mr Grant was gay and his manager then mentioned this in conversation to another member of staff. Mr Grant raised a Tribunal claim, alleging that he had been the victim of harassment and discrimination on the grounds of sexual orientation. The Tribunal upheld the claims but the Employment Appeal Tribunal overturned this on the basis that the Tribunal had failed to give adequate reasons for their decision; Mr Grant appealed to the Court of Appeal.
The Court of Appeal made clear that even though Mr Grant did not want his sexuality to be made public at his new office, and was upset that it had been, the fact his manager revealed his sexual orientation could not amount to harassment as neither the effect or the purpose of the disclosure could be said to "amount to a violation of dignity, nor can it properly be described as creating an intimidating, hostile, degrading, humiliating or offensive environment". Accordingly there was no harassment. The Court of Appeal found that the Tribunal had erred in not taking into account the fact that Mr Grant had been open about this sexuality while at the previous office; this fact was key as it significantly reduced the level of detriment suffered by Mr Grant as a result of the disclosure.
This case seems to be authority that where an employee has made public the fact that they are gay, they cannot later make a claim of harassment based on disclosure of that fact provided that there was no intention to harass the claimant by making the disclosure. The impact of this decision will also be felt in a wider sphere as it emphasises the need for a harassment claim to be based on more than trivial upset to the Claimant.
Employers should though be very careful in this sort of situation and always comply with the general rule as set out in the ACAS Guidelines to avoid any issues as it is very clear that outing a gay employee in different circumstances could well amount to unlawful discrimination.