@RobbieBaron Thank you so much. I am so grateful for your expert help. I've attached photos of the old extension lead held together so you can see what I was trying to explain.
You were right! the red and white wires were correct. For some strange reason they didn't want to work in the opposite terminals. I thought that telephone wires didn't have any polarity. Maybe I just didn't get a tight enough connection. Here's the wired socket as I tested it. Now I just need to "unwire" it, fix it to the wall, re terminate and of course tidy up the wires cutting back the green and blue one like you explained. Job done! Hurrah !!!