Spring is a fab time to come to the U.K. It is usually very verdant and nature is busting out everywhere. The weather is never predicable in the U.K. last week we had the hottest day on record at 40 (104F) degrees. On Tuesday it didn’t rise above 15 (59F) degrees. So def bring layers and rain gear. You are primarily in Scotland so visit https://www.visitscotland.com website. Scotland is usually colder than England especially on the East Coast. There is a lot of Viking history in the places you are visiting as the cruise visits the areas the Vikings had strongholds apart from Dover and London.
August is the main school holiday season so it can be busy. September is also a good time to come.
There is lots to do in Liverpool, including heritage stuff and the Beatles.
Belfast is also great, the Titanic Experience is excellent https://www.titanicbelfast.com/experiences/?gclid=Cj0KCQjw54iXBhCXARIsADWpsG_zSb2Nr57-62qDMFE0T-XaH-IyMqsQeeM86xWIHclrP0zo8byto4YaAkLiEALw_wcB
Dublin is also a fab place.
I’ve only been to Dover to catch a ferry as it’s our main ferry port to France. It’s famous for its castle. Dover is not too far from Canterbury- with a medieval cathedral.
I hope you enjoy visiting the U.K.
I don’t know how long you’ll be docked in Liverpool. If you have a late sailing you might have time to get a train over from Liverpool to York. Well worth a visit. It’s history is Roman, Viking, Medieval walls surround the city and it has a beautiful Cathedral (Minster)