Britain could seek a temporary customs union with the European Union after Brexit, the government said Tuesday as it prepared to publish its first detailed proposals on the future partnership.

Britain says its membership of the EU customs union, which currently allows for the tariff-free movement of goods, will end along with its membership of the single market when it leaves the bloc in March 2019.

The Department for Exiting the EU said it will seek to agree a "time-limited period of implementation" to provide certainty for businesses and allow for new customs arrangements to be set up.

"One possible approach would be a temporary customs union between the UK and the EU," it said in a statement, ahead of the publication of the full paper later on Tuesday.

Experts have warned it will be extremely difficult to negotiate a new EU-UK free trade agreement before Britain leaves the bloc -- particularly as Brussels has so far refused even to start trade talks.

It says there must be broad agreement first on three key issues -- Britain's financial settlement, the issue of expatriate rights, and the question of the border between British-controlled Northern Ireland and Ireland.

Britain will publish its proposals on the border issue on Wednesday, ahead of the third round of Brexit negotiations in Brussels at the end of the month.

Officials in London believe the border is inextricably linked to the customs issue.

After Brexit, the Irish border will be Britain's only land border with the EU.

There are fears that the reintroduction of physical checkpoints could upset the fragile balance of peace in Northern Ireland.

Britain's membership of the EU customs union precludes it from striking its own trade deals, and the government made clear Tuesday that such freedom was crucial to its post-Brexit plans.

"During this interim period, which will be negotiated with Brussels, Britain will look to negotiate bold new trade relationships around the world," it said.

The statement added: "Our goal is to secure as frictionless trade as possible with the EU alongside the ability to forge trade deals around the world."

However, opposition Labour lawmaker Chris Leslie, from the campaign group Open Britain, said the proposal represented "wishful thinking of the highest order".

"It is a fantasy to pretend we can have the freest and most frictionless trade possible with our largest partner when the government remain intent on pulling Britain out of the customs union," he said.