When it comes to the EU referendum, British diplomats serving Queen and country have a duty to be neutral like other civil servants. But in the world of diplomacy, “neutrality” can be a flexible concept.

With polls showing that those for and against the UK’s continued EU membership are evenly matched, UK embassies on the Continent have embarked upon a mission to sign up the country’s expatriate community to vote. And with Britons living in places like Tuscany or the Dordogne among those most likely to be adversely affected by a “leave” vote, actively helping them to have their say could prove decisive to the end result.

In France, which is thought to be home to up to half a million UK expats, the British embassy has launched a competition to encourage UK citizens to register to vote.

In an innovative scheme, the Paris embassy has tweeted a proposition: anyone who registers and posts a picture of themselves online will be offered the chance to win “afternoon tea” at the Hôtel de Charost, the 18th-century palace that is home to the British ambassador.

Registering online “only takes five minutes – the time it takes to make a cup of coffee or eat a croissant”, the British embassy said. “All we are asking people to do is encourage others to vote by tweeting photos of themselves holding a sign or poster saying ‘#YourVoteMatters to @UKInFrance’,” it added. “The most creative or unusual image will win! They may be on top of a ski slope or walking through the Catacombs of Paris: the possibilities are endless!”

Other embassies across Europe, including in Ireland, Germany, Poland, Austria, Denmark and Spain, are also gearing up for the poll which could some as soon as June.

The Madrid embassy will start its campaign to find voters on 1 February.

“Interest in the referendum among expats is high, but awareness that they may be able to vote is low,” an embassy spokesman told the Financial Times. “We want as many expats as possible to know that they may be eligible to have their say.”