It definitely generates useful amounts of power, especially in the summer. The problem is that we still need gas plant, and the distribution infrastructure ready for the rest of the year when it isn't so effective.

In the last year, 2.11% or 308 MWh of our electricity came from solar: https://app.electricitymaps.com/map/zone/GB/12mo/monthly

By way of comparison, that same source shows Germany generating 2.16% (527 MWh) of its electricity from solar so its pretty similar: https://app.electricitymaps.com/map/zone/DE/12mo/monthly