This is a quick size comparison: (for a webfriend)
The Rolls Royce Armoured Car here is 1:56 (or 28mm).
The figure (Valiant Miniatures) is 1:72, often equated to 20mm.
Gamewise these are just about useable together, particularly if you base the figure appropriately.
However, I do understand that Valiant Miniatures are large-ish compared to other 1:72 manufacturers so the size mismatch may not improve.
Can anyone help here?