Pretty stupid push-fit question

I would say it was the fitting.

Matt, he can cut the pipe with a hacksaw as long as he trims off properly. It is clear you don't know this sort of thing.

from memory ... which might be fallible ... it was about 1969~1970 ish that the change over from English measurements to metric measurements happened in copper tubing. [pendants note: there ain't any such thing as 'Imperial' linear measurements! -Albert restricted his messing about to volumetric/weight thingies equating the gallon to ten pounds et.seq. throughout the Empire. the linear measurements of inch, foot, yards, et.al remained unchanged]

I think it was probably later than that. I installed central heating in my previous house in 1969 using 1/2" and 3/4" copper pipe - and there was not even a hint of metric sizes then as far as I can remember.

Towards the end of the period in which inch sizes were used, there were several revisions to the standard - with progressively smaller wall thicknesses - so you had to make sure you had the right bending spring - and the thinner walled stuff was more difficult to bend without kinking.

There is very little late 1960's early 1970s new build around here. I therefore probably only encounter it in places that had substantial work done in that period.

I've found so many different styles of compression fittings in metric I can't identify pipe by what's used on it. The bottom line is the size: