Brian, perhaps squadron leader not an official army rank, but definitively a common name for, well, an officer leading a tank squadron. Other army branches use name squadron for (sub)units as well.
See
https://www.iwm.org.uk/collections/i...ject/205188289
Full account of Lt. Turner's capture on 28 Dec 1942 here:
http://www.warlinks.com/armour/11_hussars/11huss_42.php (just scroll down to that date).
Regards,
Leendert