>You will be compensated for your time, the inconvenience of having blood tests and procedures, and your travel expenses. The total amount compensated will be approximately £235 - £625 depending on the exact number of visits and whether any repeat or additional visits are necessary.
They deliberately do not pay large amounts, because the money is not supposed to overly-incentivize the participation, to avoid ethical issues where someone might choose to participate in something very unsafe only because the reward seems so large.
It's kind of like non-pay electoral offices. You only get candidates that can afford not to work. In medical trials, you get the kind of people that are willing to, for example, get infected with the common cold and have you blood drawn 6x a day for 4 days for about 80 bucks a day. It was not horrible, but often uncomfortable. Study recruiters still call me, and now that I have a decent paying job there is no way I would ever consider doing those kinds of studies again. Simply not worth it.
Thinking otherwise is willful ignorance, and this is clearly exploitation of lower income groups.