The welder will charge £40 per visit and if it takes an hour and a half for this particular plumber to carry out the pressure test on the radiator and then refit it, he will charge £120, making a total of approximately £160 to put right. I do not, however, want this plumber back in my house again!
Not in as many words but it was on his suggestion that a welder should attend which he then proceeded to arrange. He did, however, ask that I pay the welder separately (£40).
He instructed the welder. The money I paid him was for work done to date.
Thank you so much for your prompt replies and excellent service. My mind is a lot clearer on this issue now.