Christmas is the season of unprotected sex, according to a study.

The report cites as evidence a rise in abortions and sexually transmitted diseases in the New Year.

It also reveals a peak of births - particularly outside marriage - nine months after Christmas.

There was another, smaller peak indicating increased unprotected sex during the summer holiday period.

The report's authors are calling for seasonal sexual health campaigns, along the lines of Christmas drink-drive advertisements, to counter the trend.

Sex statistics

The study, published in the Journal of the Royal Society of Medicine on Tuesday, analysed data from the Office of National Statistics, the Public Health Laboratory Service and condom manufacturers.

They studied figures for births, abortions, incidence of STDs and condom sales from 1990 to 1996.

Birth statistics were divided into those that occurred within marriage and those outside. Births outside were less likely to come as the result of a planned pregnancy, the researchers said.

The team found similar trends for each year, pointing to an increase in unsafe sex in the run up to Christmas, with a smaller increase in summer months.

They found that:

• The UK abortion rate is highest every year between January and March;
• The number of people going for HIV tests is highest in the first quarter of each year, rising again slightly in late summer;
• Condom sales reach their greatest peak just before Christmas, with a smaller rise in early summer;
• The UK birth rate tends to rise in September, nine months after the Christmas holiday;
• The September peak is even more pronounced in births outside marriage.

The research was conducted by Kaye Wellings and colleagues at the London School of Hygiene and Tropical Medicine.

They say the findings indicate a need for better provision of contraception advice at these key times.

International trends

The trends are not unique to Britain.

In places where New Year is a bigger festival than Christmas, or Christmas is celebrated by the Julian Calendar (on 7 January), the peak in births follows slightly later, in October.

Alison Hadley is national policy officer for Brook Advisory Centres, which offer free advice on sex and contraception to young people.

She said the findings reflected the organisation's experience - the centres see more people around Christmas and the summer holidays.

She called for a three-pronged campaign.

"Beforehand you say recognise what's going to go on - take your condoms, get your contraception sorted out, be prepared.

"At the time, reinforce the emergency contraception message, so if you don't use the condom or make a mistake you know where to get emergency contraception.

"If you haven't managed to do that, get a pregnancy test as soon as you're worried, and get infection screening as well."

She said the organisation would rather the first stage worked alone, but if it failed then the other stages could act as a "fallback".

Because it was difficult to access advice services over the extended Christmas holiday, she said, it could be useful for women to have a "morning after" pill ready just in case.

"It would make a useful backstop," Ms Hadley said.