The dealer is wrong. Yes, the electrical standards did change a few years back, but that did not remove the requirement for the fridge output to be ignition switched.
The ideal solution (which accommodates both old and new caravans) is to wire as follows:
1 - Reversing lights
2 - Ignition live (old wiring battery charge) 
3 - Ground 
4 - Permanent live (caravan 12v electrics with switch in the 'car' position)
5 - Spare 
6 - Ignition live (fridge) 
7 - Ground (fridge ground return on newer caravans.) 
 Pins 2 and 6 should both be 'ignition live' but must be switched separately so that they are not left connected to each other when the ignition is turned off. If they are left connected, the fridge will drain the battery on a caravan with the old style wiring.
 Pins 3 and 7 should be independently connected to the vehicle chassis ground. One should not be 'patched' into the cable for the other.
 Though some people wire pin 5 to pin 6 at both car and caravan ends to prevent overheating of pin 6 with high power fridges.
So it's off back to the dealer to tell them they're wrong. If they still want to argue the point, then then ask them to check with an NTTA approved towbar specialist. UK NTTA - National Trailer and Towing Association
If you can't be bothered arguing, then this should be easy enough to DIY if you purchase a 'voltage sensing split charge relay.' Towsure â***8364;***8220; Towbars, Camping and Caravan Equipment
are usually cheap enough.