Once you had a basic income like this it would have the nice effect of then being able to talk about (and implement) other policies in a revenue-neutral way.

For example a government interested in reducing CO2 emissions could introduce a tax on motor fuel of say £1/litre and balance that with an increase of the basic income of £75/month.

The purpose of the UBI is to replace welfare systems by ensuring every citizen receives roughly enough money for the average person to live off. Paying everybody nowhere near enough to live off [and keeping the welfare state in place] doesn't tell us very much about how they would respond to that. Though one advantage over the small scale studies would be finding out how much citizens push back against even a comparatively small tax rise to pay for it....

Let's vote for the candidate which will give us the most money... seems like a slippery slope