I will like to find out if Mastercard test selection engine is compulsory for UK user integrators. Could you please advice?
The first place to reach for support to answer this questions is at the local financial institution since it has a connection with payments, taxes and credit card operations.
Additionally, look on the UL Transaction Security website where you can find an article that deals with this kind of items.
They also have a tool for this job: https://www.ul-ts.com/catalog/offerings/test-tools/payment-test-tools/acquiring-and-transaction-processing-test-tools/collis-brand-test-tool/c-29/c-1720/p-186