get them to confirm they own the meter Mike, then demand they supply a like for like, fit for purpose, or they will be held responsible for any issues, post expiration date for the safety cert. ..
AND why have they allowed their equipment to remain in service beyond it's serviceable life span ???
they should have addressed this matter looong before expiration (usually 10 years on a 3ph meter) ...
also is it a safety cert. or calibration cert. ...
if the latter you want a check meter installed for min. 4 months operating in parallel with the existing one, to ensure you have not been overcharged for any substantial period (how have your bills been - as expected??)
as said earlier, I had issues with bills years ago and the check meter proved an excess of 10-12% read on the existing meter
they must've forgotten you Bob ... didn't think there were any of them left (incidentally - manufactured by a company called Hookham & ???)