Charity face probe over links to Brown.
The Smith Institute are under investigation for the second time in five years over their relationship with Labour. The think-tank, who work on education policy, are a registered charity.
Strict rules mean they are not allowed to have a political bias but the institute have held 160 events at the Chancellor's Downing Street residence since 1997.
The charity also employed Brown's right-hand man Ed Balls as a researcher before he became an MP at the last election.
The Charity Commission said: "The decision was taken in the light of new information we have received which raises concerns about some of the charity's work." Senior Tory Chris Grayling sparked the investigation with a complaint to the Charity Commission and welcomed the probe.
A spokesman for the Smith Institute stressed they were fully co-operating with the inquiry and insisted they will be cleared of any wrong-doing.