sorry Jim I will not re post in this , I have repect for you and in no way am I saying you are wrong but we can only go on the information that we have and the OP has posted that he has grey PE pipe fitted in the 30s and it is 17mm, it can not possibly be fitted in the 30s Durapipe was not even thought of thenIan, the op said "In my house I have a 17mm grey plastic cold feed water pipe" hence my reply it could be Durapipe, he stated the age of the house not the pipe.
Metric PE pipe is measured by the Outside Diameter .