British Postal Agencies in PANAMA
The British Postal Agencies in Panamá City and Chagres were opened 1842 and the former remained open until 31st March 1921. It appears that all mail to and from the Pacific coast was handled (either in closed bags or individually) in the Panamá Transit Office, the first hand stamp (HS O) used in this office is recorded for 1841. Between 1845 and 1855 a transit duty of two reales was charged to the British Post Office for every Colombian ounce of mail carried across the Isthmus. A postal convention between Britain and New Granada was signed in Bogota on 17th December 1847 and remained in force with minor changes until 1st July 1881, the date on which Colombia joined the United Postal Union (U.P.U.). In 1847 the Republic of New Granada consisted of what are now the Republics of Colombia and Panamá.
This context was taking from the Book British Postal Agencies.
1847: Panama (New Grenada) entire to England, red British Post Office "Panama JA 25 184 A" backstamp (last digit of year date missing, but by looking at the arrival h.s. there is a partial "7"), red London arrival, manuscript "2/-" rate, soiled crease
1849: Panama Agency, red wax seal impression showing British coat of arms and "Panama Agency" on reverse of entire to London, British office "Panama SP 25 1849 B" split ring postmark, red London arrival and manuscript "2/-" rate, very fine and rare.
1858: MARITIME MAIL to USA via the British PO at EL Callao. Entire stampless dated in Lima, August 27 that is 26 days after Peru instituted the mandatory use of national stamps for mails abroad. It was taken directly on board; prepaid only to Panama and the 20c was due for steamship mail arriving from Panama. The black "PAID-TO-PANAMA" applied by the British Post is scarcer than the same marking in red.
1859: Iquique, Peru Oct 1859 dateline on folded letter to London, England, three line "PANAMA 6 NO 1859 TRANSIT" datestamp, manuscript "2/-" rate, red London arrival backstamp.
1859: Panama (New Grenada) entire to England, British Post Office "Panama AU 8 1859 A" split ring backstamp, red London arrival, manuscript "1/-" rate
1862: Colon, Colombia entire to London, entered the mails with British Post Office "Colon JY 23 1862 1" split ring backstamp, red London arrival backstamp and manuscript "1/-" rate, crease and age stain, very fine strike.