They had been using the new contraceptive device Persona, launched six months ago, a small monitor that measures a woman's hormone levels and indicates when she can make love without conceiving.
It was hailed as the biggest breakthrough in contraception since the Sixties and the Pill (it was once said that the three greatest benefits for women this century were the Pill, the vote and the washing machine).
But those who think the Pill is the be-all and end-all of contraception are wrong. It is only one of a long line of devices the human race has invented to avoid conception. Attempting to distance sex from procreation has led humans over the centuries to embrace crocodile dung, dried beaver testicles, poisonous mercury and Coca-Cola.
It has been argued that the first recorded attempt at contraception goes as far back as the book of Genesis. There, Onan tried to avoid family complications when asked to sleep with his brother's wife by practising the withdrawal method. For his efforts he "displeased the Lord wherefore he slew him", according to Genesis 38.
But the earliest recorded contraceptive invention dates back as far as 1850BC, according to the Family Planning Association. An Egyptian papyrus of the time detailed ingredients for a vaginal pessary made of honey, soda, crocodile dung and a gummy substance. History does not relate how effective it was - or indeed whether any man was attracted to users as a result.
A few centuries later the fashionable had dumped the dung for a more aesthetically pleasing medicated lint vaginal sponge, which was soaked in a mixture of acacia, dates and honey: a scientific combination - acacia ferments into lactic acid, which is still in use as a spermicide today.
Intra-uterine devices (IUDs) also go back 3,000 years, when women used well-shaped pebbles, although by Casanova's time the more sophisticated were using a half lemon as a cervical cap. (Casanova, incidentally, ate 50 oysters for breakfast every morning and swore by British contraceptives, according to The Ultimate Irrelevant Encyclopedia.)
Even oral contraception is nothing new. Chinese women used to knock back mercury in small doses, whereas in Canada in the 16th century, women drank strong alcohol laced with ground beavers' testes.
Women in the remote Appalachian hills of Virginia and North Carolina are still reputed to crush seeds from cow parsley and mix it into a glass of water, which they drink immediately after having sex.
Tests on mice have shown that the seeds contain chemical compounds that block the production of progesterone, the hormone that prepares the uterus to receive and nurture the fertilised ovum.
Last year's visit of the Toronto-based History of Contraception Museum to Britain revealed some of the more bizarre contraceptive devices, which 64-year-old Percy Skuy has devoted the past 30 years to building up - including amulets made from the bone from the right half of a black cat, worn round the neck to ward off conception; dried weasel's testicle, strapped to the thigh; even a plug of wax from a mule's ear.
For a more modern alternative, a Harvard University study in 1969 found that Coke had sperm-killing properties. The study was commissioned after reports that the drink was often used as a douche in countries where contraceptives were in short supply. Diet Coke was found to be the most efficient of the Coke varieties for this purpose.
No discussion of contraception would be complete without that Johnny- come-lately, the condom. In fact, that's not true - the Egyptians used them, although their animal gut sheaths were not for contraceptive purposes but to prevent against injury and infection. It was also a way of judging the class of your lover, with different styles denoting different social status.
Condoms were allegedly given their name by Dr Condom, a court physician in the time of Charles II - who, judging by his many illegitimate offspring, did not always employ them. Highly prized ones were made of sheep gut with a pink ribbon round the end; in the 18th and 19th centuries pornography frequently decorated the most expensive.
It was not until 1843 and the invention of crepe rubber that the condom was transformed, and not until the Thirties that latex was used.
The most modern interpretation is perhaps Karl Machhamer's "liquid condom", in which liquid latex is applied. Instructions are much the same as for traditional condoms but some users complain it takes too long for the latex film to dry; the inventor recommends using a blow-dryer to speed the process up.
As a footnote, here is a lesson for linguists and those planning national birth control programmes. In 1976 a Dr T Healy wrote in the prestigious journal Science that contraception was playing a role in the spread of sexually transmitted diseases in Scandinavia. While gonorrhoea had declined in Sweden it had not in Denmark. Dr Healy put this down to the fact that while the Swedes have a simple word, kondom, the Danish was svangerskabsforebyggende middel. The tongue-tied Danes bought fewer.