KEJA said:
.... the towing limit is 1400kg as it states in the handbook, so assuming this is 85%, this means the weight of the car is about 1650kg.
No, the there is no direct connection between kerbweight and towing limit. The towing limit is determined by the car manufacturer by carrying out physical tests according to set procedures, which include, but are not necessary limited to, the provisions of the EU Directive relating to towbar equipment. It is totally independent of the car's kerbweight, which may be higher or in some cases even lower than the towing limit.
KEJA said:
.... so what is the actual law on towing, either its 85% for all or anything up to 100%.
The law is the manufacturer's towing limit, not 85% (which is only a recommendation by various sources) nor 100% (which only applies to driving licence entitlement with a Category B licence, but not to actual legal technical towing limits).
Note also that the towing limit is not the MTPLM of the caravan, but only its axle load, i.e. the MTPLM minus the noseweight, which is not 'towed' but 'carried' by the towcar.