London Late Fee & Too Late Mail (GB)
A Study of the London Late Fee & Too Late Posts of the 1800's - Roger Marsh
For a detailed study of the handstamp types used see the GBPS LPHG London Late Fee and Too Late Mail 1840 to 1930 pdf by Parmenter which will open as a download.
Late Fee 4d rate To complete the set of boxed fees here is an L4 to Spain, 6d postage and 4d Late fee. The 4d late fee rate was used to August 1869 with the boxed L4 first used in December 1868.