Currently, the '15-year rule’ means that up to four million long-term expats, roughly half of whom live in Europe, cannot participate in UK elections. The Conservatives promised in their 2015 manifesto to abolish the rule, but despite pressure from campaigners, the Votes for Life Bill has not yet materialised.

Now, a number of expats represented by London law firm Leigh Day will issue urgent judicial review proceedings in the High Court today, arguing that the EU Referendum Act – which excludes those who fall under the 15-year rule - breaches their rights under European law.

The proceedings could see the In/Out vote, scheduled for June 23, delayed while up to two million extra names are added to the register of voters.

Richard Stein, a lawyer from Leigh Day, commented that the act ‘arbitrarily excludes are those UK citizens who are among those most likely to be affected by the decision taken by voters in this referendum’. He added said Brexit could affect expats on issues including health care and pension rights.

‘Not to allow them to vote on the decision whether the UK remains part of the EU is unlawful and we have asked the court to deal with the issues urgently so that the act can be amended before the June date, to include all UK citizens residing in the EU for however long.’ Sources: The Telegraph; Financial Times