A "Prevent" ban on extremist speakers at universities is "unlawful", the Court of Appeal has ruled.

The Government has been forced to partially revise its counter-terrorism strategy after senior judges decided that the guidance was not balanced and accurate enough.

Muslim campaigner Dr Salman Butt won a Court of Appeal challenge against part of the Prevent Duty Guidance, which states: "When deciding whether or not to host a particular speaker, RHEBs should consider carefully whether the views being expressed, or likely to be expressed, constitute extremist views that risk drawing people into terrorism or are shared by terrorist groups."

Master of the Rolls Sir Terence Etherton ruled that the guidance, issued under the Counter Terrorism and Security Act, was unlawful and should be quashed.

The judge said it was not "sufficiently balanced or accurate" to inform higher education institutions of their duty to ensure freedom of speech when deciding whether to host a speaker.

Sitting with Lady Justice Sharp and Lord Justice Irwin, Sir Terence said redrafting that part of the guidelines was a matter for the Government.

But the court dismissed a challenge by Dr Butt regarding the process by which information about "extremists" is collected, stored and used by the Extremist Analysis Unit (EAU).