On 17th September 1974 the Vanden Plas 1500, based on the Austin Allegro, was introduced as a replacement for the Princess 1300. Powered by BL's 'E' series 1485cc overhead camshaft engine fitted with a single SU HS6 carburettor producing 68bhp at 5500rpm, purchasers had the option of a 5-speed manual gearbox or 4-speed AP automatic.

The model was fitted with Hydragas independent suspension. The Mark 1 model did not receive the picnic tables on the rear of the front seats as seen on the Princess 11/1300s and rear legroom was somewhat limited compared with its predecessor. However highly polished burr walnut was used on the uniquely designed facia and door fillets, the seats were trimmed in leather, bound Wilton carpets over extra sound deadening covered the floor and the cabin roof was trimmed in nylon cloth. Externally the car received a scaled down Vanden Plas radiator grille, extra bright work around each window, twin chrome door mirrors, stainless sill trims, and rubber faced bumpers. 3640 Mark 1s were produced before the Mark 2 model was introduced in October 1975. 

Mechanically the Mark 2 cars received revised suspension settings giving a much better ride. The engine and transmission remained unchanged. Internally the rear seats were altered and moved rearwards giving extra legroom and, due to customer demand, picnic tables were fitted as standard to the rear of the front seats. Externally the Mark 2 was fitted with black plastic sill protectors, full width wheel rimbellishers and thinner chrome trim around the front and rear windscreens. 7318 Mark 2s were produced before the Mark 3 model was introduced in October 1979.

The Mark 3 models received slight name changes. The manual transmission model retained the 1485cc engine but now received twin SU type H1F4 carburettors which increased the power output to 77bhp at 5750rpm. This car was now called the Vanden Plas 1.5.  The automatic transmission model now received the 1748cc 'E' series engine fitted with a single SU type HS6 carburettor giving a power output of 72bhp at 4900rpm. This car was called the Vanden Plas 1.7

Externally the Mark 3 cars differed by having a flat boot lid, black surrounds to the front and rear windscreens, black door mirrors and side indicator repeaters fitted to each front wing. Internally a radio and front seat headrests became a standard fitment and the interior door handles were now black instead of chrome. 

The Vanden Plas factory at Kingsbury closed in July 1979 with all remaining cars being finished at MG Abingdon. Production of the Mark 3 ceased in August 1980 after a production run of 752 manual and 232 automatics.