Image copyright PA Image caption Theresa May has rejected calls for a Commons vote before Brexit talks begin

The government must set out in detail what it hopes to achieve from Brexit talks in order to restore public trust in politics, a senior Tory MP says.

Andrew Tyrie called for an "early, full and detailed explanation" of the government's negotiating position.

The public's "sky-high" expectations about the financial savings from Brexit had to be managed, he said.

Meanwhile Boris Johnson has insisted defence and security co-operation would continue despite the UK's exit.

Ahead of a meeting of European foreign ministers in Slovakia, the foreign secretary said "we may be leaving the EU, but we are not leaving Europe," adding that the government is "absolutely committed to participation in European foreign policy, defence and security cooperation".

Speaking during a visit to Austria earlier, Mr Johnson said the UK was seeking a "new European partnership" with the EU's remaining 27 members

Mr Tyrie, the chairman of the Treasury Select Committee, backed Remain in June's poll which resulted in a Leave victory.

He is now urging ministers to "cast aside the damaging claim and counter-claim" of the referendum period.

In a pamphlet written for the Open Europe think tank, Mr Tyrie said the referendum's "pernicious legacy" was to add to a "deep distrust in politics".

"Politicians cannot afford to allow this to get any worse," he said, saying the government had to be frank about the "trade-offs" involved with Brexit - "and the fact that many of the promises made by the Leave side are manifestly unfulfillable".

He added: "Equally unfulfillable are the hopes of many Remainers, that the UK can carry on pretty much as now, and that a renegotiation can achieve continued membership through the back door."

Clarity

Parliament should get the opportunity to approve the UK's negotiating position before Article 50 of the Lisbon Treaty - which begins a two-year exit process - is triggered, Mr Tyrie said.

Prime Minister Theresa May has rejected this option.

Image copyright PA Image caption Andre Tyrie backed Remain in the EU referendum

Mrs May has said she will not trigger Article 50 until the start of next year at the earliest, while some Brexit campaigners have called for it to be done immediately.

According to Mr Tyrie, the government should wait for "clarity" from other EU partners on what they will be able to offer, which could mean delaying Article 50 until German elections in September 2017.

Mr Tyrie, who based his article on evidence given to his Commons committee, said the negotiations over Brexit could secure "meaningful economic and political gains" but risked "early and possibly severe damage" if not approached properly.

He said Britain should aim to negotiate "extensive access to the single market, some degree of influence over its rules, withdrawal from the customs union, and the restoration of control over free movement", entrenched in a treaty with the EU.

Free movement

Alongside access to the EU's markets, Mr Tyrie also said "far-reaching" change was needed to the free movement of people. Curbs to migration have been the key demand of many Brexit campaigners.

Image copyright Reuters Image caption Boris Johnson says he has a vision of a "new European partnership"

EU leaders have stressed that single market access is dependent on accepting free movement.

But Mr Tyrie said: "The idea that ultimate UK control over migration can be restored without fatally compromising the UK's trade relationship with the EU is not unreasonable.

"Purism by EU negotiators on this point would not only be inconsistent with reality; it would also clash with other member states' economic interests."

The government needs to be clear that curbing immigration could carry an economic cost for the UK, "controversial though saying this remains", he added.

'Open Britain'

In other Brexit news, a new campaign group is being launched to succeed the Britain Stronger in Europe group, which led the unsuccessful Remain campaign.

The cross-party Open Britain group said it would push for continued membership of the single market while making a positive case about the benefits of immigration - "mending not ending" the free movement of EU citizens into the UK.

The organisation says it has the backing of 500,000 registered supporters across the UK and the endorsement of senior Conservatives, Labour and Lib Dem politicians.

"Getting the best deal for Britain means starting the negotiations with ambitious goals," said Tory MP and ex-business minister Anna Soubry, one of the group's spokespeople.

"The campaign will marry a commitment to Britain's membership of the single market with making a positive case about the benefits of immigration.

"The present system needs further reform. It's particularly important people know the facts about immigration, we tackle their concerns and ensure the system works fairly for everyone."