2 pairs of water pliers and give it a nip up...
If it’s no good you could isolate the tap - undo the nuts and stick a bit of ptfe tape around the olive (just 2 or 3 wraps should do it.)
Then tighten the nuts back up. If it still leaks call a plumber. If you’re in shropshire area i’ll happily give you a hand if i find myself close enough one day. You’re probably looking at a £40 job if you call someone out and catch them on a good day.