Boris’ argument may indeed be wingnutty: it’s also wrong.

Foreign sportsmen pay UK taxes on appreaance moneys and tournament winnings earned in the UK.

I think it’s only FIFA and Olympic events that don’t, which requires special contracts, maybe even laws.

Of course Andy Murray would not have tried harder if the headline tax rate was lower. I think Boris is misunderstanding something else he has heard. The issue is a sportsperson who comes to the UK to compete are not just taxed on appearance fees and winnings won while in the UK. The tax authorities also want a proportion of their worldwide endorsement earnings from outside the UK. UEFA have said it was unlikely to offer finals to the UK for that reason.The Government agreed to waive the tax for this year’s Champions League final at Wembley. Usain Bolt withdrew from a UK event because the UK tax authorities would have taxed him on global earnings.

The best athletes will still come to the absolute top prestigious events even with the tax. However, the tax situation is a disincentive for those just outside the top athletes in other sporting events held in the UK.

Amusing as usual from Boris, but its a fair point! We do need lower taxes and in the long run it would benefit everyone.
But I can’t believe he is suggesting cutting VAT. I would like to see it cut in the long run because 20% is too high, but I don’t pretend it would do anything for consumption. Everyone laughed at Labour when they cut VAT to 15% and said it would have to go back up (sure enough it did), frankly it did sod all then, and would do sod all now, apart from cost us money.