My Daughter, SIL and I did the British Isles on the Regal Princess last June/July. I think Princess had more interesting stops. That being said, we enjoyed Liverpool and did the HOHO bus. Lots of interesting stops and liked that all the museums were free admission. In Belfast we did the Antrim Coast & Glens. It was a very misty, chilly day but the views of the countryside and the sheep everywhere was amazing. If you can get an itinerary that includes Edinburgh, you won’t regret it.
We stayed two nights in London and wished we stayed longer. Did the bus out of Victoria Station on Embarkation day and it couldn’t have been easier. Handed bags to bus person and didn’t see them again until we were in our cabin.
Enjoy but be prepared for cold rainy weather.