The think tank, which describes itself as being "centre right" and believing in a "small state and strong society", told Third Sector in June 2006 that it was seeking charitable status.
But 12 months on, it still does not have charitable status, despite the Charity Commission's 87-day timetable for registrations.
A spokesman for the commission confirmed the application was still pending.
He said that every case was looked at in light of charity law, but added: "What it does as an organisation, if it's not run-of-the-mill, might make it more complicated."
It is not unusual for party-affiliated think tanks to be registered charities. Earlier this year, however, the commission warned that its ongoing enquiry into the Smith Institute and its relationship to the Labour party could have consequences for other think tanks.