Brexit Secretary David Davis has said he "doesn't have to be very clever" to do his job.

Mr Davis told LBC radio that intelligence was not the principal requirement of his position leading the Brexit negotiations. "I do just have to be calm," he said, adding that when the agreement fell apart on Monday he had come close to losing his cool.

"What's the requirement of my job? I don't have to be very clever, I don't have to know that much, I do just have to be calm," he said. "And that did test the calmness a bit, a little bit.

"But we had to pick another day and we looked at Wednesday but Wednesday wasn't long enough for the DUP to sort themselves out so we made it Thursday, Friday morning."

Mr Davis was appearing after his interview with the BBC's Andrew Marr on Sunday, in which he said the agreement with the EU was not "legally enforceable" and was contingent on a succedsful trade deal. Those provoked a response in Ireland, for whom the agreement represents a guarantee preventing a hard border returning to the island of Ireland. Irish Prime Minister Leo Varadkar called the agreement a "cast-iron" guarantee that was "politically bullet proof."

He was also asked about the recent furore in which he was forced to admit that 58 sector-by-sector Brexit impact assessments do not exist.

"In the last 18 months I've talked about impact here and there, but an impact statement, this is a thing that the Labour Party have been going on about, an impact statement has got a proper meaning in Whitehall, there's a definition of it and so on, including things like forecasts.

"Now I don't actually believe economic forecasts, they have all been proven wrong, I mean look at all the ones about Brexit.

"So what we do is we look at what we call a sectoral analysis which is the size of the thing, the size of the industry, employment levels, how much is dependent on Europe, how much is dependent on European regulations, how much opportunity there is in other countries.