The Britannia is a below street level pub, there are two entrances, one opposite Monument in Monument Street (the main) the other just around the corner in Fish Street Hill, interestingly  Fish Street Hill has an excellent historical pedigree, getting a mentioned in Pepys diary, Saturday 29th October 1664, "... by appointment to the King’s Head tavern upon Fish Street Hill, whither Mr. Wolfe met me to discourse about the Fishery" I think being named the King's Head may have been a better choice than The Britannia, but no matter, tis done now.
The pub is a good size, there are fruit and gaming machines along with a pool table,  despite it being a Wednesday the place was pretty busy, the majority enjoying the food, which is typical pub grub at reasonable prices. There was no queue at the bar, but the ale front was somewhat disappointing, the Pride was off, leaving Adnams which ran out before the pint was pulled, there was a large range of lagers, but I gave them a miss and popped into the Monument for a pint of Old Bob.