A post-Brexit UK-EU trade deal might take 10 years to finalise and still fail, Britain’s ambassador to the EU has privately told the government.
The BBC understands Sir Ivan Rogers warned ministers that the European consensus was that a deal might not be done until the early to mid-2020s.
He also cautioned that an agreement could be rejected ultimately by other EU members’ national parliaments.
No 10 expressed confidence in reaching a deal to suit the UK and the EU.
In October, Sir Ivan, who conducted David Cameron’s negotiation over the UK’s relationship with the EU, advised ministers that the view of the 27 other countries was that a free trade agreement could take as long as a decade.
He said that even once concluded, the deal might not survive the process of ratification, which involves every country having to approve the deal in its own parliament.
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It is also understood he suggested that the expectation among European leaders was that a free trade deal, rather than continued membership of the single market, was the likely option for the UK after Brexit.
Sir Ivan’s private advice contrasts with ministers publicly insisting a deal can be done in the two years allowed by the triggering of Article 50 – the formal start of the process of leaving the EU.
Downing Street said he was relaying other EU members’ views, rather than his own or the British government’s.
A spokesman said: “It is wrong to suggest this was advice from our ambassador to the EU. Like all ambassadors, part of his role is to report the views of others.”
By Laura Kuenssberg, BBC political editor
Just how long will it take?
The government is intent on persuading us Brexit can be done smoothly, and to time.
So the suggestion that the UK’s most senior diplomat in Brussels has privately told the government that a final trade deal with the rest of the EU might not be done for 10 years, and might ultimately fail, may give rise to more nerves.
Read more from Laura
Dominic Raab, a former minister and a Leave campaigner, told BBC Radio 4’s Today programme that Sir Ivan “was the diplomat who persuaded David Cameron to dilute his ambitions for the renegotiation which was one reason why the referendum was lost, so he’s been scarred by his own pessimistic advice in the past”.
“It’s reasonable to set out the worst case scenario for a five to ten year period to iron out a trade deal. The key thing is whether we maintain barrier free trade in the meantime in which case frankly there’s no problem – we leave the EU in 2 years we complete the free trade agreement afterwards.”
But Remain-backing former Lib Dem leader and ex-deputy PM Nick Clegg, said: “I worked with Ivan Rogers in Brussels on trade deals 20 years ago. He knows what he is talking about – the government should listen.”
EU leaders are preparing to meet in Brussels – and will discuss Brexit negotiations at an end of summit dinner, without UK Prime Minister Theresa May being present.
Downing Street said Thursday’s meeting showed the EU was facing up to the reality that the UK was leaving.
It is expected that the other members will discuss who will the lead the EU’s negotiating team in Brexit talks.
This is expected to be former EU Commissioner Michel Barnier, who is in charge of the European Commission’s Brexit team.
‘February at earliest’
In other Brexit developments on Thursday the House of Lords EU financial affairs sub-committee has warned that financial services firms could quit the City of London unless there are transitional arrangements, or a “Brexit bridge” to prevent them moving to New York, Dublin, Frankfurt of Paris.
Meanwhile, UK Brexit Secretary David Davis told MPs on Wednesday that the UK’s Brexit plan was still being worked on and a lot of research had to be done before it was ready.
He said the UK would not spell out its negotiating aims in more detail until February at the earliest.
But a senior EU official has said the 27 member states are sticking to the principle of “no negotiation without notification”, meaning talks can only begin once Mrs May has triggered Article 50.
She has said the UK will formally notify the EU of its intention to leave by the end of March at the latest.