Thread by @ChrisGiles_

Extraordinary evidence at Treasury committee from Jon Thompson, CEO of HMRC on customs and Brexit today

The Brexiter favourite Max Fac - would cost business between £17 and £20bn a year

- that's almost 1% of GDP

- just for filling in forms

Thanks #Brexit

How does he arrive at the figure

200m export consignments at an average cost of £32.50 each = £6.5bn (times two because two way traffic)

plus around £4 to £7bn of rules of origin compliance from filling in other forms

Theresa May's New Customs Partnership is much cheaper for business (almost zero cost) because it seeks to replicate today's arrangements but is thought to be "cretinous" by brexiters and "magical thinking" by the EU27...

...and

Mr Thompson said he did not expect the EU to reciprocate over the customs partnership.

What that means is UK collects tariffs for EU and hands it over when a ship lands in Felixtowe and drives to Calais, but if ship first lands in Rotterdam, EU keeps the import tariffs.

Both would not be ready by 2021. Max Fac needs 3 years. Customs Partnership requires 5, Mr Thompson said.

The border would be "functioning", but if technology not ready ministers would need to trade off their objectives of "free flow, revenue and security".

Leaky borders

"We think we can manage the risk - we think we can" he said. He didn't sound so sure.

And "the potential backdoor risk applies to both models" he added

Didn't sound like officials think either is sensible