I don't know if it helps, but I noticed this in the book, The Worshipful Company of Gunmakers A History. The UK Proof House self published it in 2008, edited by Stimpson.
"It became clear in 1992 that with many standards of conducting proof being detailed on an international basis it was essential that the Proof House should be modernised and furnished with the latest electronic measuring equipment. By December 1993 the planning stage was complete and, in order that work could continue, a temporary Proof Chamber was erected for use just as had been done, long ago, in the year 1757.
...All work was completed by September [1995]."
I also noticed the following comment about the CIP. "in June 1980 the UK became a Member State. The immediate result was that British proof procedures were required to conform fully to CIP standards and decisions".
