I honestly don't know if CEF use the same company to do all of their calibration days around the country,
(probably not at a guess?)..
But for example this company ACS
https://www.acs-calibration.co.uk/ state on their website..
Calibration Days
ACS offers a unique calibration opportunity, holding calibration days on-site in different locations throughout the UK. These will be held at your local branch of City Electrical Factors (CEF).ACS representatives will be on location on the specified days and will be able to show you the very latest state-of-the-art test equipment, which is required under current legislation. The onsite 'drop-in' service has been designed, to make it quick and easy for you to get your equipment calibrated. There will also be an opportunity to take advantage of many special promotions that are available for test equipment from leading manufacturers.
and they also say they can offer same-day drop off & collect..
On-site Calibration Day
An on-site calibration day is where our engineers attend specific branches on scheduled days with our mobile calibration facility. This enables you to call in with your test equipment, get them calibrated and pick them back up later that day. Or if required while you wait! Therefore making it simple for customers to get equipment calibrated, without it being out of service for too long.
There is a contact button on their website so may be worth asking?
I have never used them or CEF for any calibration services.. So can't offer any first hand experience and/or costs!!
But..
Many years I used a mobile guy, who would offer on-site calibration at wherever you were..
until he stopped doing his mobile service..!!
Then I used an old forum sponsor Specialist Instrument Services ISSWWW...
https://isswww.co.uk/calibration Because they had a branch within 20-25min drive from me..
and could do same day drop-off & collect calibration service..
But then the branch was closed down!!
I dislike sending any meters away via post for calibration as it just adds more delays plus the risk of loss/damage in transit!
My most recent calibrations have been carried out by a small local company who are within 10 miles of home..
So I can easily arrange a mutually convenient drop off and collection date/time..
Their last charges were approx £65 for a Multi-function meter and £35 for a single function meter, (plus VAT).
Hope that helps to de-mist some of the Calibration clouds!!?