The Allegro was introduced in 1973 to replace the best-selling Austin/Morris 1100/1300 model. The two smaller Allegros carried over the A-series engines but models with larger engines were added using the 1500 and 1750 E‐series from the Maxi. There was also an up-market version – the Vanden Plas 1500.

Apart from the usual transverse engines and front wheel drive, the car had Hydragas fluid/air suspension. Early cars had the 'Quartic' square shaped steering wheel but it was dropped after two years.

This sectioned Allegro was probably assembled in BL's Seneffe plant in Belgium. Acquired by BMC in 1965, Seneffe built up cars for the European market, such as the Mini and Allegro, from CKD kits which arrived from the UK.