Appearing on Newsnight, the former director general of the World Trade Organisation, reiterated a deal would be a “complex, bumpy and nasty” process and was likely to last between five and seven years.
Speaking from Davos in the Swiss Alps, the European Commissioner for Trade between 1999 and 2004 said an interim agreement would need to be secured first before main negotiations are underway.
Pascal Lamy says Brexit deal won't happen before 2019
UK will be a third country like Mexico, like Japan
He said: “Yes I still hold that view. It’s going to be complex, bumpy and nasty like any trade negotiation, we know that by experience. Unless we invent the first ever trade negotiation in history, which would be a love affair, I don’t really believe it can happen.
“UK will be a third country like Mexico, like Japan. So, UK has to negotiate the terms of access to the EU market and EU has to negotiate the terms of access to the UK market, it’s seven for the size of the EU market to one, which is the size of the UK market.
"It’s going to be complex, long, it’s probably a good thing, a better thing than going back to the WTO tariffs.
"But it will take time and inevitably trade will be less open than when the UK was a member of the internal market.”
Wark put it to the former director general that Mrs May was determined to invent something and didn’t want an “off-the-shelf deal like Norway”.
Also that certain sectors, such as financial services and the car industry, might strike separate deals within the EU.
David Davis is confident of securing a 'good deal' with the EU
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Mr Lamy said: “There will be no separate deal. It’s a single undertaking. You have to agree on everything before you agree on anything and there’s no deal, which would be a sector deal. This will be toughly negotiated on both sides.
“The main difficulty for the British exporter to the EU continent, whether goods or services, like financial services for instance, accounting, will be the UK will have to match EU regulations and standards without having any say on this regulation and standards. That’s a big problem for the future.”
Brexit Secretary David Davis has said Britain would complete its deal to leave the EU in a “year or two”.
But a pessimistic Mr Lamy, who was director general of the WTO from 2005 to 2013, ruled out the possibility of the UK securing a EU deal before 2019 and that laws could be separated at the same time a trade deal was done.
Michel Barnier, the EU's chief negotiator, will take charge of the Brexit negotiations
He added setting up a team of negotiators would be a long and costly process for the UK.
He said: “What I know is that, like any other EU member, UK disbanded its trade expertise when it was transferred to the European Union, so they have to re-constitute a whole body of trade experts and trade negotiators.
"This will inevitably take time and, by the way, be pretty costly and at least that’s what I’m told by my friends in the consulting and the legal business.”
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‘I don’t know of any trade negotiation that lasted less than five to seven years, which means that there will need to be a sort of interim arrangement, which will have to be negotiated before.”
In response to Boris Johnson’s recent outburst that warned French president Francois Hollande against administering “punishment beatings” similar to a “World War Two movie”, an unimpressed Mr Lamy labelled it an embarrassment.
He said: “What Boris Johnson said today leaves me to wonder whether it’s Donald Johnson or Boris Trump. It’s a clear embarrassment for all these high-flying diplomats in the foreign office and they deserve all our compassion.”