While looking for something else, I came across this:
"Note: As of late 2009, Punch Taverns have [sold] the Britannia to Ashmole Investments, property developers who plan to redevelop it to create "residential and investment opportunities". We're not sure when it will finally be closing."
Yes they were, as was the Crown in Blackfriars Rd but that's just changed hands and the people who were in there at the end of September had only been there a month. That leads me to think that the company, the Only One Pub Co, or something, were maybe leasing or renting from Punch.
Perhaps BigPhil, who's just announced his arrival at the Crown, may be able to shed more light...
Britannia is (well was byt the sound of it) owned by Only Pub Services (www.onlypubservices.com). I've asked the landlord to confirm whether this is true and not a name mix-up but have not heard back yet.