Very cool, if true

I think the question was asked in the wrong way - it's a big leap from "Yes I would be willing to pay more tax to fund the NHS" and working out how much spare income one actually has to pay it. If I were answering the survey I would probably put down £100 as it would not require me to make a big commitment of time to the question. In practice I could probably pay a lot more and would be willing to do so if everyone else at the same level of earnings were paying the same. You then ask "But how much more?" and I reply that I would actually need to do a lot of working out to get to a sensible figure.