How did you get on? That one was a bit tricky. Here are my thoughts.
Consider
COLREGS to apply are;
With this type of question, if you are not sure or are unable to map it out in your head just yet, pop it down as a picture, the answer will be relatively clear. I teach a traffic light system, if it was at night and you could see their red light - do something about it, if you could see a green light, stand on with caution. Why with caution? Simply because they may keep coming as in this case. I have had many occasions when there have been some very splendid vessels in and around the marinas I have visited who’s owners have had no formal qualifications and are self taught. That said, there have been many that were well versed in the rules that apply to them, sadly there are a few that have no idea. Don’t forget, to operate in the UK, you do not need to have any form of licence to buy or drive a boat, but that is a very different question that may appear sometime in the future so I won’t ruin it by giving the answer here.
Have a great day.