Sir Ed Davey, leader of the Liberal Democrats, walked into the Brixton Donor Centre with every intention of doing his civic duty. He filled out the paperwork. He rolled up his sleeve. And then the NHS politely told him: sorry, but your holiday to the south of France has made you a temporary biohazard.

It turns out that a jaunt to the Charente region, while lovely for the soul, is less lovely for the blood supply. The NHS has decreed that anyone returning from certain parts of France between May and November must wait four weeks before donating, thanks to the risk of mosquito-borne viruses like Chikungunya and Dengue. Because nothing says 'summer holiday' like 'potential vector for a tropical disease.'

A Liberal Democrat spokesperson confirmed that Sir Ed will return once the 28-day quarantine - sorry, 'waiting period' - has passed. His visit was part of a campaign to beat the 'winter crisis' in the NHS, which is a bit like trying to fill a bathtub with a teaspoon while the drain is open.

NHS Blood Donation says it needs over 140,000 new donors this year to meet demand. Blood has a shelf life of 35 days, so it's not like they can stockpile the stuff. Earlier this year, the NHS warned of 'a significant shortfall in blood stocks' due to hot weather, holidays, and high demand. In other words, the perfect storm of people being too busy sunbathing to bleed.

Gerry Gogarth, director of blood and plasma supply at NHS Blood and Transplant, said: 'We urgently need anyone eligible to donate to book an appointment as soon as they can.' And if you're not eligible because you've been to the French countryside, well, there's always next month.

The restrictions apply to a rather specific list of French regions: Bouches-du-Rhône, Charente, Dordogne, Hautes-Pyrénées, Haute-Garonne, Pyrénées-Orientales, Var, Gard, Hérault, Isere, Alpes-Maritimes, Vaucluse, and Corsica. So if you're planning a holiday that involves both sightseeing and blood donation, maybe pick somewhere with fewer mosquitoes.

Sir Ed's spokesperson said: 'Ed unfortunately could not give blood today due to recent changes to rules regarding blood donations after travelling to certain destinations. He'll be back.' And we're sure he will be - armed with a calendar and a healthy respect for insect-borne pathogens.