“These envelopes were produced as a stopgap measure to facilitate the prepayment of postage by Members of Parliament following cessation of the Free Franking System and the introduction of the Uniform Penny Postage on 10th January 1840, the adhesive labels (stamps) and the Mulready envelopes and letter sheets intended for general use not being available.
“The first envelopes, which were printed in black and bore the heading Houses of Parliament, were made available on 16 January but within two weeks specific envelopes appeared inscribed House of Commons (also printed in black), and House of Lords (printed in red). These envelopes, which remained in use until the introduction of the 1d black and 2d blue adhesive stamps and the Mulready postal stationery on 6 May, were only valid for postage if posted at the Houses of Parliament but a few are known cancelled outside.”