AndyBuckley wrote
The roundels are correct for Battle of Britain markings; the later style roundel with the thin yellow and white rings wasn't introduced till mid 1942.
The Spitfire pictured in formation with the Tucanos is wearing Battle of Britain markings.
Battle of Britain Memorial Flight - Spitfire P7350 (Mk IIa)
Battle of Britain Memorial Flight - 92 Squadron - Geoffrey Wellum
You can see the correct roundel ratios on the Global Aviation Resource article.
Global Aviation Resource
A very early roundel modification produced the following strange result, but it still differs considerably from the roundel on the camo Tucanos. It appears that something has gone wrong with the roundel ratios on the camo Tucanos.
http://i152.photobucket.com/albums/s...ppy35/Tuck.jpg
From following forum.
Robert Stanford Tuck Spitfire Mk V
You can see the roundel ratio on QJ-F at the following link
http://www.techmod.pl/techmod/images/48000/48001-02.jpg
TJ