Again thank you all for your advice and support...
I settled with the plumber today, I simply offered to pay him half of what he billed us for (which is still more than he should have gotten anyway, but the sums weren’t huge and I wanted to get this sorted rather than have it drag on). He admitted sending the guy to my house last week but said he only asked him to deliver some invoices and nothing more, if the guy was abusive or asking for money then he did so on his accord.
This is a load of rubbish obviously, there is no need to deliver invoices by hand at 9pm, it could have been posted or put through the letter box, but as I decided to settle I told him I wasn’t going to go into this and we just exchanged a cheque in return to him signing a ‘full and final settlement’ document.
Now a new problem emerged, the electrician (a mate of the plumbers BTW) came up with a funny bill, got offended when I told him it was way OTT, so now we are in dispute with him... no idea how I got involved with these type of people

I never had anything like it in before... I will report back when I have an update.
But for now many thanks again to all of you.