The Alvis TB 21 was a series of limited production roadsters introduced in 1951. Much like the Alvis TB 14, the TB 21 was built on an Alvis TA 21 platform, but featuring an open body built by coachbuilder AP Metalcraft. These roadsters were powered by the same 3.0L inline six engine as the TA 21, but with a different carburetor, which increased power to 90hp. Only a total of 31 examples of the Alvis TB 21 were built, with production ending in 1953.