As a Brit, I reckon Brexit, and the restricted access to ESA [0], are the far more reasonable explanations here...
[0] https://www.gov.uk/guidance/uk-involvement-in-the-eu-space-p...
[0] https://www.gov.uk/guidance/uk-involvement-in-the-eu-space-p...
"The UK’s membership of the European Space Agency (ESA) is not affected by leaving the EU as ESA is not an EU organisation."
I think you meant the EU Space programme, but that does not seem related to military imaging satellites.
Also, even large cities have places which are better to target
It is not. The UK, like most nuclear armed states, has a "No first use" doctrine, meaning its nukes exist only to retaliate, to turn cities to ash.
Whoever is nuking you, to the point that you use those retaliatory nukes, might be targeting your weapons, but they are on submarines in friendly waters, so not likely to be destroyed before they can launch.