The UK to Brasil route has been littered over the past half-century with a series of failed airline operations, of which British South American Airways was probably the first and the demise of Varig only the latest. It's not the gold mine route many think.
There's not a lot of high-yield business traffic, but in addition to traffic potential the instability of the local currencies has led to all sorts of difficulties getting funds back to the airline's base. And if you can't get at the money your passengers gave you, what's the point?
It's these same currency issues that have done down many Latin American airlines over the years.
Rio is no longer the main destination of choice in Brasil, what business traffic there is tends to be concentrated on Sao Paolo.