Lobby briefing - Tradução em português
Downing Street responded to the criticism at its weekly lobby briefing shortly after Prescott accused the government of presiding over the development of labour camps following revelations that unpaid jobseekers on the government's work programme were asked by the Close Protection UK (CPUK) security firm to sleep under London bridge before stewarding the Queen's diamond jubilee celebrations over the weekend.
I have not read this expression before, Simon, but I understand it to mean a "briefing that takes place in a lobby". In other words, an informal meeting with members of the press corps (jornalistas). And I say "informal" because a lobby is not the street and yet it is not the main part of a building. It is in between. It is certainly not where a formal meeting would normally take place.