Turns out the £660bn "national cost of UBI" quoted here is the result of Cllr @RossMackinnonWB simply multiplying the UK population by the UBI they'd get, without factoring in the additional tax revenue coming back to HMRC.

In other words, he's confused gross and net costs. https://twitter.com/WBerksCons/status/1334624092478115842

A modelling exercise for @openDemocracy found that a full UBI would have a gross cost of £438bn. But after factoring in the money coming back in tax, the net cost would be only 15% of that – £67bn.

The gross cost of any UBI proposal is meaningless. https://www.opendemocracy.net/en/beyond-trafficking-and-slavery/basic-income-could-virtually-eliminate-poverty-in-the-united-kingdom-at-a-cost-of-67-billion-per-year/

Here's the working out from Cllr Mackinnon's (public) Facebook page.

The £660bn figure just doesn't add up.