De Havilland Mosquito: An Illustrated History - Ian Thirsk - Google Books
The link states the second of two special pre production aircraft, Sea Mosquito TR Mark 33, TS449, was fitted with props of 12 feet 6 inches diameter (Type D/14/445/2). Reason seems to be the 4 blade gave 5 to 10% greater thrust than the 3 blade, an advantage for the limited take off run on the carrier deck.
Edited to add; have been reading through a number of flight test reports on various Mosquito versions and it seems 12 feet was the standard 3 blade diameter. The high altitude 3 blade paddle prop seems to be 12 feet 6 inches. Others mentioned were 12 feet 1 inch 3 blade and 12 feet 4 blade (latter fitted to F Mk XV high-altitude, pressurised fighter). Whether they all were standard fit or experimental was not made clear, though report preamble seemed to suggest standard.