Hi - that is exactly what i remember as a kid - i clearly remember the rear derailleur and now yo have put the image above I recognise the front derailleur as well. It gives me a great starting place to go shopping !!
As a side note asked on Facebook about the make and we might be getting somewhere some one said:
I have a small collection of head badges including one of these, The Service. I think it came from the Wearwell Cycles factory at Alverley where my father worked for a while'
So it would not have been a 6 speed - what would be the most fitting rear block to put back on it? Thank you to everyone for the help so far!