LONDON (Reuters) - Britain set out on Tuesday how it plans to keep European Union laws during its transition from the bloc after next March, saying elements of the 1972 laws which make Britain a member of the bloc would need to be saved, including a role for the European Court of Justice (ECJ).

FILE PHOTO: Anti-Brexit demonstrators wave EU and Union flags opposite the Houses of Parliament, in London, Britain, June 19, 2018. REUTERS/Henry Nicholls

It issued a policy document on legislation it says is needed to implement the terms of any final exit deal negotiated between London and Brussels, once it has been approved in principle by parliament.

The document is the most clear presentation yet of how the government intends the relationship between Britain and the EU to be little changed during the so-called implementation period until December 2020.

It sets out a continuing role for the ECJ throughout the transition and for EU laws still to apply.

“As part of delivering a smooth and orderly exit, the UK and EU have agreed that during the implementation period the existing EU mechanisms for supervision and enforcement will continue to apply to the UK,” the Brexit department document said.

Brexit secretary Dominic Raab said keeping EU laws was necessary to provide certainty during the exit process.

“Our view is that repealing and saving the effect of the ECA (European Communities Act), for the time-limited duration of the implementation period, is the most effective way to provide continuity and certainty to businesses and individuals,” the document said.

The government first announced the legislation now known as the EU (Withdrawal Agreement) Bill late last year, saying it would allow more parliamentary scrutiny and oversight of the policies set out in the withdrawal deal Britain is hoping to strike with the EU.

The plan is to start debating the new bill once a withdrawal agreement has been agreed with the EU and approved by way of a vote in parliament.

The bill is expected to cover issues such as any agreement on citizens’ rights and a financial settlement, and the details of an implementation period agreed between both sides.

However, the extent to which the bill goes into detail on these policies, and the scope it will give MPs to actually change policy remain uncertain.

The key element of the withdrawal package is the future relationship Britain and the EU agree to seek. This could be a broad outline rather than detailed policy for lawmakers to pick over, and as such may not be in the bill.

Details of the document can be accessed here. here