Franking Privilege and the Penny Post

An MP had the franking privilege while he was an MP and while Parliament was sitting.  This allowed him free postage in the General Post, either on mail that he had franked (signed) or that was addressed to him.  However the franking privilege did not apply to Penny Posts which had to be paid.

Here are two examples in the Taunton Penny Post, the top from 1817 when Sir Thomas Buckler Lethbridge was not the MP for Somerset, so he had to pay the full postage (10d in the General Post plus 1d in the Penny Post), and the bottom from 1821 when he was an MP, so he only had to pay the Penny Post.