LONDON (BLOOMBERG) - EU migrants entering Britain during the Brexit transition period of about two years will be allowed to live, work and study as under current rules.

But when Britain finally exits the bloc they will face restrictions from bringing family members with them, Prime Minister Theresa May's spokesman James Slack said on Wednesday (Feb 28).

"We are taking back control of our borders when we leave the EU," Slack said. "Once the implementation period is over we will have an immigration period of which we are in full control."

The announcement is a watering down of May's position last month in which she vowed to fight the EU to enforce a difference between rights for European nationals who arrive before Brexit day - on March 29, 2019 - compared with those coming during a transition.

Migrants staying for more than three months will have to register. After five years, migrants can apply for permission to remain.

After the transition period, at some point in 2021, family members will have fewer rights.

Currently a family member can come to Britain if a migrants earns at least £18,600 (S$34,214) a year and that could be in line to rise.

Slack said he expects other EU countries to have reciprocal arrangements with the EU.

The government also said it's looking at a "range of options" for a new framework on immigration, and that Brexit won't end immigration from the EU.