Former chief EU negotiator says UK government's handling of Brexit will cause damage not seen for over half a century.

Sir Michael Leigh says a post-Brexit free trade deal will take at least five years as an "absolute minimum" to negotiate.

Leigh says EU cannot trust Britain while Cabinet ministers "contradict" each other on a daily basis.

Whitehall is struggling to afford the negotiating talent it needs to deliver Brexit.

LONDON — The decisions taken by Prime Minister Theresa May and her predecessor David Cameron over the UK's relationship with Europe will be as harmful to Britain's interests as any decision the government has taken for over 50 years, a former EU negotiator has told Business Insider.

"The decisions taken by the former prime minister David Cameron, exacerbated by the decisions taken by his successor, are the most harmful decisions that have been taken by a British government for decades," Sir Michael Leigh, who was a European Commission Director-General from 2006 to 2011, told BI.

"You have to go back to the Suez crisis in 1956 or to Munich in 1938 to find decisions taken by a British government that will turn out in time to have had such negative consequences for the United Kingdom." The Munich pact, signed by Britain and France, gave Hitler the go ahead to invade Sudetenland, Czechoslovakia, and led former Prime Minister Neville Chamberlain to declare "peace of our time." Britain went to war with Nazi Germany a year later.

Leigh served as the European Commission's Director-General for enlargement from 2006 to 2011 and during that time was the European Union's chief negotiator with countries seeking to become member states. He is now based in Brussels and is a senior adviser to American public policy think tank, German Marshall Fund.

In an interview with BI, the former EU negotiator echoed concerns expressed by other former diplomats, including Sir Simon Fraser and Steven Bullock, that May's government is both unprepared and ill-equipped for divorce talks with EU negotiators.

"The negotiations in any real sense of the word haven't really begun. They are preliminary exchanges and discussions as to methodology so no one can really say we've entered fully-fledged negotiation yet," Leigh explained.

"However, it's clear that the Commission has used the full period since the notification under Article 50 to prepare detailed position papers. While preparations may be going on in Whitehall and in Autumn the British side may put forward a whole series of detailed negotiation positions, until now that's not the case.

"The general impression is that Britain has not used the time since notification to prepare detailed negotiating positions. The main reason for that is division among Cabinet ministers as to the approach to be taken and of course, that's exacerbated now by the loss of the government's majority and therefore the loss of authority for the prime minister."

Cabinet division is ruining the chances of a Brexit deal

One of the big problems hindering progress in Brexit discussions, Leigh claims, is the difficulty facing the EU in trusting the British government when it is so obviously divided over so many key issues.

"The main reason is divergent statements by leading British political figures," the former negotiator says.

Barnier has got to be concerned that anything Davis says on any given day could be contradicted the next day by another Cabinet minister.

"Michel Barnier [chief EU Brexit negotiator] may notionally have David Davis in front of him as his negotiating partner, but if senior Cabinet ministers go on record almost every day with divergent positions on key issues like the single market and transitional arrangements, then it's a fact that the person opposite Barnier does not have the authority to take a clear and sustainable negotiation position.

"Under these conditions, Barnier has got to be concerned that anything Davis says on any given day could be contradicted the next day by another Cabinet minister.

"As long as that remains the case, then it will be very hard, even if there is trust in personal terms, to establish full trust in negotiating positions.

"All this might be clarified in September if clear negotiating positions which have the full approval of the Cabinet are put on the table. If this happens then things could begin to improve."

A free trade agreement within two years is "impossible"

Another big issue the government is struggling to deal with is a civil service simply not up to the task of delivering Brexit. Whitehall lacks the "institutional capacity" to deliver Brexit, Leigh says, and is struggling to persuade talent to join its ranks. An Institute for Government report published in November warned that the workload presented by Britain's departure from the 28-nation bloc posed an "existential threat" to some Whitehall departments.

"As is well known, for well over four decades now Britain has not had to have a team of its own trade negotiators," Leigh explains. "So the government has gone looking for talent in New Zealand and Canada and is trying to attract people — but isn't always able to pay the salaries to attract them. There is a lack of institutional capacity in Whitehall in terms of the trade side of things."

If the two sides are able to "establish good will and mutual trust" then there is no reason why a divorce agreement — including Britain's financial obligations and rights of EU citizens — can't be settled within the time period allowed by the Article 50 notification, Leigh says. However, a post-Brexit free-trade arrangement, which Cabinet ministers including Davis and Liam Fox have suggested can be negotiated before Article 50 talks conclude, will take half a decade at the very least to finalise, he claims. He also stresses that while the Article 50 period on paper lasts for two years, Britain, in reality, has little over 12 months to agree on the terms of its departure. This is because time must be set aside for EU Parliament to ratify the deal.

This prediction echoes that of Steve Bullock, who last month described the idea of a post-Brexit free trade deal being negotiated within two years as "absurd" in an interview with BI.

"It might be possible during the two years to sketch out in very broad terms the nature of the future relationship and on the EU side," Leigh says. "But this can only be discussed once the Council has decided there has been sufficient progress on the divorce settlement. For example, they could agree that the future arrangement should be a deep and comprehensive free trade deal.

Brexit Secretary David Davis. REUTERS/Francois Lenoir

"But it would be impossible to reach an agreement in this period on the long-term relationship itself.

"Experience shows to negotiate the kind of agreement that Mrs May is talking about — a far-reaching, ambitious agreement — five, six, seven years have been needed in the past to negotiate comparable agreements. Even if this could be shortened a little bit, I don't think you could expect a long-term agreement to be in place before five years as an absolute minimum. And one has to consider that this must be ratified by all the EU's member states. In Belgium that involves eight parliamentary assemblies."

Britain must accept all EU rules in any transition deal

A key talking point in recent weeks has been whether UK negotiators will be able to secure a transitional arrangement to fill the gap between Britain dropping out of the EU in March 2019 and a long-term deal coming into effect.

The Cabinet is reportedly in agreement that a transitional period is needed to protect the economy from falling off a cliff, but divisions remain over what a temporary arrangement should entail. Hardline Brexiteers are reluctant to accept any transition deal which means the continuation of current UK-EU migration rules. However, Leigh insists all EU rules, including the free movement of people, would more than likely have to continue as part of any transition deal.

"You could also reach an agreement on transitional arrangements provided that the British side was ready to accept that the transition period would be a stand still — i.e. the whole of the EU's laws would continue to apply once Britain had left, " he explains. "That could be agreed. For one year, two years, renewable or otherwise.

"But what could not be agreed during this period is a pick and choose arrangement where Britain would choose parts of [membership] but not others. That would require detailed negotiations that would be more lengthy and go against the principles from the EU's point of view.

"Beyond that, one has to be clear about negotiating objectives and to begin to talk about transitional arrangements, for example, it has got to be a transition towards something. As there is no consensus yet on what that thing would be, this is another consideration that has held up negotiations on the British side."

Britain's rejection of the EU is "astonishing and depressing"

Leigh, who was knighted for his services to EU in 2012, says the Brexit vote has caused sadness among colleagues who have spent years representing Britain in EU institutions. "The single market was largely a British creation," he says. "It was created by Mrs Thatcher together with her right-hand man Arthur Cockfield, Commissioner at the time, working together with Europe to put into place the single market, which British Conservatives, liberals and others strongly advocated.

"So for people like myself and others who for years have worked on the single market, to see this landmark British accomplishment being rejected by a later Conservative government, is astonishing and depressing."

Brexit has not actually happened yet. We are only beginning to feel a trickle of the economic effects.

Unlike some European leaders, though, Leigh doesn't believe there is any real chance of the decision being reversed, as the British public won't "wake up" to the negative effects of Britain's departure until it's too late. "It's just really sad," he says, with a tone of regret in his voice.

"As things stand today, public opinion has not yet woken up to the full costs of Brexit that will actually pan out over a decade or more. There's a kind of an inebriation with the fact that initial estimates of the impact of the economy have not yet been realised, but of course, Brexit has not actually happened yet. We are only beginning to feel a trickle of the economic effects.

"It will take time for the public to realise that in one area after another, the public goods that they've been taking for granted and that have been provided by the EU, gradually will disappear. In one field after another — from aviation to agriculture to fisheries to education to food safety — you can go through the whole range of areas where the EU rather quietly has for decades been providing good regulation. It will take a good deal of time and expense for the UK itself to replace these and set up its own regulatory arrangements to provide the same public goods. But it's going to take time for people to realise all of this and by the time they do it'll be too late.

"It seems unlikely to me that there'll be a major shift in public opinion in the next 13 months that'll convince a British government to actually reverse the decision either by a parliamentary vote or by a second referendum. You can never say never in politics but it seems to me highly unlikely."