Liam Hennessy (Pierce Brosnan) is clearly based on Irish politician Gerry Adams. Adams was actively involved in the Irish republican movement, although he denies having been a member of the IRA (a claim contested by many). He later became the leader of Sinn Féin, the political branch of the IRA, and was heavily involved in establishing a lasting peace accord in Northern Ireland. Hennessy even shows physical resemblance to Adams (short gray hair, full beard, glasses).
The trivia items below may give away important plot points.
In February 2016, two reports were made to the London Metropolitan Police about a "terrorist attack" made on the Lambeth bridge, after many local citizens were not told about a controlled stunt explosion made on a double decker bus for this film.
Quan only kills the IRA members involved with the bombing that killed his daughter, not any of Hennessey's men that try to stop him. He also doesn't kill the only female member, Maggie, who is instead killed by the police.