The Brexit secretary, David Davis, last week convened 33 UK business leaders to Chevening: a place I know well, as it was the grace-and-favour house that my husband, Nick Clegg, used when he was deputy prime minister. The setting was particularly well chosen, as Chevening is, despite the hard work and dedication of the staff, an unusual combination of grandeur and dysfunctional nostalgia (I well remember the running battle to get the most elementary wifi service installed).

Here, according to the Financial Times, British business leaders were asked to share the table with the Legatum Institute, a thinktank with unparalleled access to Davis and Theresa May and that seems to have been at the origin of some of the preposterous positions on Brexit taken by the government so far. Its inexplicable presence at that table was the clearest signal that the government has not changed its views on Brexit after the general election even one tiny little bit.

The institute has established a special commission on trade that consists of more than 20 people with different “trade” backgrounds. It is run by a British American director. The Legatum member who has just been nominated the UK’s new chief trade negotiation adviser is a New Zealander. The funding of the institute comes from a foundation that is part of a Dubai-based private investment group. So much for the UK “taking back control”.

Unlike thinktanks like the Center for European Reform which knows more about the EU than the whole cabinet put together, the common characteristic of most of the Legatum trade commission seems to be not having worked at any time within the EU or even directly with it. I have negotiated myself for the EU on many occasions on trade, and I have seen how shocked negotiators from other countries become when they realise how difficult it is to negotiate with 27 countries – with their own institutions and legal system – at the same time.

It is easy to see why this government would be mesmerised by Legatum. It is keen on unilaterally removing tariffs and quotas on agriculture products (farmers, take note) in exchange for services agreements all over the world. The effect of this on food security and food prices was highlighted this week in a report published by the University of Sussex. Equally importantly it doesn’t take much to realise that we are going to need an agriculture market at least 50 times the size of the UK’s to secure like-for-like access in foreign markets for our much larger services sector. A thinktank that can’t even work out the respective sizes of our farming and services sectors is in dire need of a lot more “thinking”.

The institute also seems to be behind Davis’s recurrent claim that the UK will have “frictionless” access to the single market even if it is not part of it – an embarrassing comment that brings despair to Europeans, as the single market is a system of rules based on trust and a single legal order, and therefore accessible only to those who are part of it. When the EU negotiator Michel Barnier says that “some in Britain still do not understand”, he seems to be referring among others to how Davis still has not understood this.

The main idea of the institute, though, seems to be the creation of a “prosperity zone” between the UK, Australia, New Zealand and Singapore, eventually extended to the US, Canada and Mexico, if the North American Free Trade Agreement renegotiations succeed. This is actually an old idea, originally floated by Mitt Romney in 2008. It obviously did not work then, and it will not work now. One does not need to have a Nobel Prize in trade economics to realise that, even with the US and Canada included (which is very unlikely indeed) this can hardly compensate for all the trade that the UK will lose by stepping out of the EU.

The best thing this government could do to appease the serious concerns of UK business leaders on Brexit is to rely on the business leaders themselves. This means no more toying with extravagant and ill-founded ideas. And it also means seeking an interim arrangement with the EU to continue benefiting from the single market and the customs union for as long as is needed until an alternative EU-UK deal is reached, as business leaders have proposed. This can be done by placing the UK into the European Economic Area on a temporary basis, and/or looking for an ad hoc arrangement extending the current status quo. Neither the extreme Brexiteers nor the extreme remainers like this option, but it is the only sensible thing to do right now. It allows the UK government to win time. And time is what the government needs – to get the skills it misses, to draft proposals it has not even started to draft yet and to negotiate with the serenity that the high economic interests at stake deserve.

An interim deal is the only way to deal with the ticking clock Michael Barnier hears because, as any trade negotiator knows, there is nothing worse than negotiating against time. Except for negotiating against time in pursuit of delusional and unrealistic ambitions.