An electronic braking system in a motor vehicle capable of towing a standard trailer not having its own EBS system has a separate pressure control channel for the generation of a trailer service brake pressure signal in the event that a driver's braking demand is sensed at any axle of the towing vehicle. The pressure signal level is set in the towing vehicle so as to be a function of the driver's electrical demand signal modified in dependence upon the load exerted by the trailer on the towing vehicle as measured at a towing link therebetween. Separate adaptive loops are provided in respect of the towing vehicle braking and the trailer braking, with the towing vehicle adaptive loop being responsive to deceleration error established by a comparison of vehicle retardation against driver braking demand, and with the trailer adaptive loop being responsive to towing link load, such as to obtain error signals which cause the adaptive adjustments to be made in the two loops in a mutually co-ordinated manner in order to achieve the required overall vehicle retardation.