Amber Rudd
Home Secretary Amber Rudd leaves Downing Street following the weekly cabinet meeting on December 5, 2017 Jack Taylor/Getty Images

Home Secretary Amber Rudd has written an open letter to all EU citizens currently living in the UK.

Concern for the future of EU citizens living in the UK has been high on the agenda ever since the June 2016 referendum which saw 52% of the UK electorate vote to leave the European Union.

A deal has since been struck that allows some 3.7m EU citizens who currently live in the UK to have full citizens' rights once Britain exits the union in March 2019.

In her letter, Rudd hoped that the fresh agreement "provide reassurance" that the government was keen to safeguard their futures.

A deal was reached after months of painstaking talks in Brussels last week, which had been derailed by rows over the divorce settlement and the future of the Irish border.

Official guidelines for the next phase of talks state that initial drafts were expected in January on how the trade discussions would evolve.

They also confirm that the UK will be leaving both the single market and the customs union, an area that still causes divisions in Westminster.

The guidelines revealed that Britain cannot sign a new trade deal until it becomes a "third country" upon exit from the EU, up until that point, all talks will be preparatory.

May's hopes of commencing trade talks seemed on the verge of collapse due to a disagreement with the DUP over the future of the Irish border, but these were also resolved.

The prime minister has however repeatedly stated that "nothing is agreed until everything is agreed", with the next stage of talks set to be the toughest yet.