To Ship to the UK, or not to Ship to the UK. You decide. Definitely look into it to see if it is viable or not for you. There are two resources below for your perusal, and I would also suggest talking it over with your accountant or a tax expert.
As I am in the Republic of Ireland, I am looking at this from the perspective of shipping from the EU to the UK. I've created a quick video below that talks through where you can find some information on the topic to help with your research, and I also show how to add and/or remove a shipping zone.
One frequently asked question is; "Can I separate Northern Ireland from The United Kingdom?" and the straight answer is no - not from within the standard Shopify shipping settings. You could use an app like Advanced Shipping Rules to create different zones and areas, however it can get messy and costly. If you do want to explore this option, reach out to the Shopify support team to talk it through.
Links mentioned in the following video;