Who is Oliver Lacon from Tinker, Tailor, Soldier, Spy and what is their importance?

Oliver Lacon serves as a senior advisor at the Cabinet Office. He lives in Ascot, which is the location for the meeting between Lacon, Guilliam, Smiley and Tarr. It is at this meeting that Smiley gathers the details of the Hong Kong affair, and the possibility of a highly-placed mole in British intelligence.