Probably just common sense but it was the subject of 2 scientific studies and papers.
http://arstechnica.com/science/2016/...in-britain/#p3
One study, authored by population health researcher Clare Tanton and her colleagues, was an examination of 12,530 people who took part in the British National Survey of Sexual Attitudes and Lifestyles between 2010 and 2012. The group was composed of people from 16-74 years old, who reported having at least one sexual partner in the past five years. Out of this group, 9.2 percent of men and 5.3 percent of women said they found one or more new sexual partners while outside England. And out of those groups, according to Tanton and her colleagues, there was a lot of "disassortative sexual mixing," meaning cross-nationality intermingling.
In total, 72 percent of men said their overseas hookups were with non-UK residents, while 58 percent of women said the same. Interestingly, the study states that "men were less likely than women to report having partners from the Middle East/North Africa (2.4 percent vs 5.7 percent)." People who had sex with non-UK residents were also less likely to identify themselves by ticking the box for "White (British)" on the survey form.
These encounters were not just snogging sessions, either. The study defined sex as "vaginal, oral, or anal with someone of the opposite sex, and oral, anal (for men), or genital contact (for women) with someone of the same sex." People who had sex while overseas were also more sexually adventurous in general; they reported having more partners both at home and abroad, as well as multiple partners and partners of both sexes. These adventurers were not always having safe fun. They were less likely than the abstinent travelers to use condoms every time they had sex and (surprise) more likely to have been diagnosed with a sexually transmitted infection (STI). They were also more likely to get intoxicated using drugs or alcohol—though not necessarily during sex.
Tanton and her colleagues suggest that these findings lead to one basic conclusion, which is that travel can spread STIs across the world very rapidly. The rate of sexual mixing suggests that populations with low rates of STIs are being exposed to ones with higher rates. For example, chlamydia transmission rates are much higher in the UK than elsewhere in Europe, so when UK travelers hook up with non-UK residents, they may act as an infection "bridge" between the two populations. The same issue arises for UK travelers exposed to STIs that are more common abroad, who come home and spread the infection locally. The researchers recommend providing information about STIs and safer sex to travelers who leave the UK.
This is especially true in the case of backpackers, who were the subject of a second study of sexual activity among people backpacking in Thailand. "Over one-third of backpackers traveling without a longterm partner or spouse had vaginal and/or anal intercourse with a new partner; one-third of these did not use condoms consistently," write medical researchers C.T. Lewis and G. de Wildt in their paper. When it came to safer sex, Brits and Swedes were the most likely to report not using a condom during their escapades.