The Briham PRH 4 was a design development from the Mk 2 in order to accommodate a new regulation 650cc Triumph engine and Manx Norton chain drive gearbox.

New bodywork was outsourced to Specialised Mouldings and the design incorporated front brakes by Mini and rear brakes by Triumph.

The car was quick when compared to its competitors and the prototype’s driver Peter Orr was often able to begin at the front of the grid. However engine reliability issues often prevented the car from finishing.

Favourable reviews by Mike Cotton of Motoring News generated sufficient interest to produce 5 further cars, most of which were sold to the USA.