The International Relations students group of the London School of Economics.
The Grimshaw Club is the oldest student society at the LSE, and gets some of the most prestigeous speakers to discuss International Relations issues - this year in particular they've had Lord Hurd former Foreign Secretary, James Rubin former Spokesman of the US State Department for example.

The reason it is called the Grimshaw club instead of the IR Society comes from it being named after a popular student member who was tragically killed by a car soon after WW2.