The severity of poverty in rich western nations is easy to underestimate. There are people in the UK who are underfed, can't afford heat, have to work multiple jobs etc. This kind of poverty does look different than poverty in India - better in some ways, but worse in others - but it is still poverty.
The data on relative poverty is hard to trust, but we also can't trust gut feelings about which countries "must" have more poverty. Perhaps it is true that UK does have a higher fraction of people in some kind of poverty.