The UK Government is facing a fresh legal challenge over its plans to leave the European Union.

A pro-EU think tank, British Influence, is writing to Brexit minister David Davis over Downing Street's plans to leave the European single market.

The group say a legal challenge is likely to follow the letter to Davis.

British Influence want clarity on the UK Government's plans to leave the European Economic Area (EEA) as part of leaving the European Union.

The EEA extends single market membership to three non-EU countries: Norway, Iceland and Liechtenstein.

Members contribute funds to some EU budgets but do not participate in areas such as the common agricultural policy nor do they have a say in decision-making inside the EU.

They believe leaving the EU does not mean necessarily mean quitting the EEA. The UK has been a member of the body since it began in 1994.

If the legal challenge is pursued and is successful, it could mean MPs have the final say on Britian's EEA membership.

A spokesman for British Influence said: "It is likely there will be a legal action because, in our view, the government has taken a stance that leaving the EU means leaving the single market."

The UK Government is currently facing a legal battle in the Supreme Court over who has the power to trigger the legal mechanism to leave the European Union.

Downing Street believes the Prime Minister has the authority to do so but the High Court ruled MPs must give their consent first. Theresa May has pledged to trigger the mechanism by the end of March next year.

A final ruling by the Supreme Court is expected in January.

Chairman of the regulatory policy institute and emeritus professor at Hertford College, Oxford, Professor George Yarrow, told the BBC: "There is no provision in the EEA agreement for UK membership to lapse if the UK withdraws from the EU.

"The only exit mechanism specified is Article 127, which would need to be triggered."

Article 137 of the EEA agreement states: "Each contracting party may withdraw from this agreement provided it gives at least twelve months' notice in writing to the other contracting parties".

A spokesman for the UK Government spokesman insisted the UK would automatically stop being a member of the EEA once it leaves the EU.

He said: "As the UK is party to the EEA agreement only in its capacity as an EU member state, once we leave the European Union we will automatically cease to be a member of the EEA.

"The future relationship between the UK and the EU will be subject to negotiations. It's not in the UK's interest to give a running commentary on our thinking that could undermine our negotiating position.

"The referendum result will be respected and we intend to invoke Article 50 no later than the end of March next year."