Re: Yeah, but...
Tim, you say the deadweight cost is lowest on sales taxes such as VAT but look at what happened with the pasty tax? Even Little Gideon was forced to back off, which indicates that the deadweight cost is actually very high. Logically, the only place a deadweight cost is low is where taxpayers have no choice but to choose to make themselves liable for the tax so that'd be things like VAT on essential items (like clothing), Road Tax (or SORN, the mere act of owning a car means you pay tax whether or not you drive it or even if it works) and taxes on heating, light, other utilities.
On those you can stick the rate up as far as you like and rake in the money, except that doing so will actually kill people long term because 20% is very high after all the other tax you pay and you have no choice. If, as the AC above says, it was 0.35% you'd probably have a lot more left than you currently do, not counting the fact of the Chancellor taking less of your actual pay.
It's a big change and I desperately want to find a reason for it to be impractical because if it IS practical then we're just self-harming as a nation by not doing it.
Some day, somebody will do a Party Political Broadcast where they do nothing except "A week in the life" highlighting how much of a normal person's wages are taken in tax. All taxes, not just Income Tax.
And if we don't do something soon, that day will be the first day of the revolution.