I think the pricing is based on coverage, usage density and demand. The UK probably has enough terrestrial coverage of amy sort that they figure they can upcharge anyone who still wants/needs Starlink, since it's mainly setup to be internet service for those who have essentially no other decent choice.

Alternatively, maybe the meaningful coverage areas are so small and dense that the price should be higher. Since Starlink's biggest limitation is that performance suffers in more densely populated areas.