Plumbing!

[Dead Eye]

You can get those replacement blanked off spigots in most large DIY stores. B&Q, Wickes, etc.

Visited both a large B&Q and a Wickes but neither seemed to stock that sort of thing. The only Stop End bits they had were for push-fit piping

It's also too late to order anything from the internet as naturally my friend has left this all to the last minute