".....Official dealer charges 10 quid for a battery change/check and does it in an hour."
I checked a similar comment about a dealer in Bahrain with Breitling UK and was told that a '1 hour battery change and check' would not be in line with Breitling's rquirements and would invalidate any warranty. Very few dealers are authorised to service Breitlings; the process takes several days as the watch has to undergo some form of power vs time check. Only when it has passed this and the case seal replaced and checked will the watch be sent out in its protective case. It is a far more complex process than just taking off the back, changing the battery and then replacing the back!
I've had the battery of my Aerospace changed three times in the 10 years I've owned it; on each occasion it took about a week and any other minor work needed was completed at the same time free of charge.
Never be tempted to have a £1500+ watch battery replaced by some back street 'while you wait' dealer!