Good news Derek, well done. Can I just ask when you counted the 20 weeks from, was it from the original phone call or from the date of your face to face? I'm in the same boat, this is my first application and still waiting after having had the f2f some weeks ago. However I did get a letter from DWP on 10th October saying they now had all the information they needed to make a decision, but I'm still waiting.
The 20 weeks was from when I received the form. I also had a letter on the 15th October, and then a decision letter on the 24th October. I hope this helps you, good luck.