Nice clock and quite collectable. The Astral trademark belonged to the well regarded firm of Henry Williamson Ltd and dates from 1910 and was used for a long time with a fusee and later a going barrel movement, Williamson made their own lever escapements. The firm subsequently became ECWM (English Clock & Watch Manufacturers) when it merged with Grimshaw & Baxter & JJ Elliott Ltd. around 1921. In 1932 ECWM was bought by Smiths who registered the Astral trademark in 1933 and continued to use it into the 1970s. Smiths is known to have made large numbers of marine clocks using the round Astral lever timepiece movement they inherited though I don't know how long production was continued from ECWM's Coventry factory after they acquired it.
The rectangular movement was available with a platform or pendulum regulation, the latter had rounded shoulders, the former square ones, they were different of different dimensions. The backplate on the one you have above obviously has a platform yet has two holes at the top for pendulum regulation so that's interesting.