Why are you talking about a UA fare in a US forum?

I'm currently on a similar UA fare at the moment. UA would have charged me $500 to cancel the ticket and $400 for any changes.

Similarly, based on your fair rules, you would have to pay 120 GBP to cancel your ticket before flying. You can change your ticket as well, but you will have to pay 120GBP PLUS any fare differential if there is one. You could conceivably get money back as well if the fare dropped. UA doesn't let you apply the refund to the change fee. You'd have to pay the 120 GBP in new money before you could get anything back.

Always read the fare rules as that is what the airline will look at when answering your questions about fees, changes, etc.

While there are fully refundable fares without fees in lower buckets, typically you have to buy a Y/B to be completely penalty free.