25% of the working age population is economically inactive (with more being below the income tax floor) most of whom do not receive benefits (they're living off savings or others) even before you actively incentivise people not to look for work. It's going to cost a lot more than £12k per taxpayer, and with median UK household income being only £27k the taper for the working poor is going to be steep, and the middle classes seeing a net tax increase is going to include an awful lot of people struggling to pay off their mortgages.

And the thing is, many people who are actively looking for work or disabled already receive more than the UBI in other benefits being cut to fund this. The true beneficiaries? Upper middle class people who've paid off their mortgage, built up savings and wish to retire a decade or two earlier and traditional housewives. The losers? The working young and single people.