I’m 49 and I’ve been married for 23 years but I’ve recently begun having liaisons with other men. I had some homosexual feelings before I got married but they have increased recently as my desire for my wife has decreased. However, I’m still unsure about the extent of my “gayness”. What should I do?

Dr Eric Dunlop, my former boss and mentor, was a senior consultant at the Royal London Hospital. He also advised the Government on sex.

Dr Dunlop had the outward appearance of an obsessional, old-school Harley Street doctor, or even of a scientist; in fact, he was the first doctor to realise the full significance of chlamydia.

Despite his rigid appearance he was fascinated by human sexual behaviour and very understanding when dealing with the emotional and domestic problems it could generate. One topic he frequently discussed was the very problem you have written about. Although peoples’ sexual interests and enthusiasms may appear to change as they get older, what is really changing is their ability to give physical expression to their sexual fantasies and desires, once their potency begins to wane.

It is a mistake to suppose that all homosexuals have the same pattern of sexual behaviour, or an identical psychological make-up. There are, for example, a few homosexual men who fear and even dislike all women and they are especially repulsed by the thought, or sight, of female genitalia. This may lead them to become misogynists. The great majority of men with predominantly homosexual interests also have some heterosexual urges. When they are young, testosterone-rich and physiologically at their peak, there is no need for them to be with a man in order to have an erection and an orgasm. A woman would be pleasing, if not equally pleasing, especially if they were aesthetically beautiful and there was good psychological rapport. One of the ways in which homosexuals were formerly categorised was by the extent to which they were “obligatory ” or “facultative”.

Obligatory homosexuals had sex only with men, even if their lives were filled with seductive, alluring women. Facultative homosexual men were those who would prefer, but perhaps only just, sex with a woman but, if none was available, would make do with a man. As Dr Dunlop used to say: “Given the circumstances, they would accept any port in a storm.”

Dr Dunlop’s analysis fits your own situation. When you were 26 you were probably not quite as testosterone-rich as you had been ten years earlier but you were still virile and libidinous. You apparently had homosexual feelings before you married. It may be that your family, colleagues and friends expected you to be heterosexual and you acquiesced. Even so, you wanted to marry and presumably enjoyed a fulfilling sex life. You are probably one of the bisexuals who is in the centre of the sexual spectrum, predominantly homosexual, but only just.

Your youthful sexual vigour allows Dr Dunlop’s “any port in the storm” theory to operate. His premise also supposes that once a man’s potency begins to fail his orientation tends to revert to whatever was his principle sexual interest when young. He suggested that many older bisexual men would increasingly often find it difficult to achieve an erection with a woman. As their sexual desires dwindled so often did other rewarding aspects of a heterosexual relationship that once had a strong sexual component.

What is the extent of your gayness? It’s impossible to say without knowing you. I’d hazard a guess that you are bisexual but predominantly homosexual. Now that you are older, and your sexual drive is ebbing, the physiological reflexes that control your sexual response need more stimulation to achieve an erection.

Your principle objectives, if you have children, should be discretion and consideration for what is best for your wife and children.Think hard before taking drastic action. Before talking to your wife, sound out her opinions on similar mythical cases. Some women are tolerant of homosexual unfaithfulness. Others are repelled.

Use a condom and tell your wife. The Thatcher Government’s iceberg advertisement campaign in 1987, to highlight the growing problem of HIV/Aids, may be a dim and distant memory, but HIV is still a chilling reality for the gay community — so be smart and play safe.

Mind you, navigating your way through sexual health is likely to be a walk in the park compared with the titanic drama you face when breaking the news to your wife.