Leafing through Chamberlain & Ellis, I can't find any Vickers Light tank (excluding AA versions) armed with anything heavier than a .5 inch Vickers machinegun.
I think this is a different series. I found some information at this website: http://mailer.fsu.edu/~akirk/tanks/ It's called the Model 1937 there, but I don't know if that is the correct designation.
According to the website http://mailer.fsu.edu/~akirk/tanks/ it belonged to a series of export-versions of the British Light Tank.
This is very interesting. It makes the light tank look like a decent vehicle! You must have a newer edition - mine has nothing on this tank, and page 85 is the American M1 / M2 Combat car!