These are known as commercial overprints. The Commercial Overprint Society of Great Britain has a website that might give you some more information.
http://www.cosgb.org/A quote from their catalogue listing:
Quote:
The Stamp Duty Act of 1853 required that a 1d. duty be paid on receipts of £2 or more; this duty was paid with revenue stamps. The Act of 1881 made it legal to pay those duties with postage stamps as well. In 1920 the duty was raised to 2d.
In order to prevent the theft of stamps intended for this fiscal use, some companies had overprints put on their stamps.
Ryan
Posted 10/25/2010 6:23 pm
