Britain’s schools have reached a ceiling of achievement because of government interference, a headteachers’ union leader has said.

Mick Brookes, general secretary of the National Association of Headteachers, made the claim in his union’s annual conference in Bournemouth this morning.

He said that while Britain’s schools have improved on the low standards of the early 1990s, “real barriers to further progress” have emerged which are preventing sustained improvement today.

“Unless we clear the decks of clutter, stop trying to implement scores of initiatives that are distracting us from these hugely important goals, even if we don’t fail we will not get anywhere near; not in this parliamentary lifetime anyway,” Mr Brookes said.

“Unless the promised sustained above-inflation funding is delivered to schools on an equitable basis some schools will be unable to deliver without raising class sizes or cutting services and staff,” he added.

Mr Brookes argued that the UK’s teaching workforce were likely a “neglected army” and called on the government to make the inspection system “less like a sword of Damocles”.

“Our message to the secretary of state is this: it is time to trust us.

“If you want us to make further improvements to children’s achievements you have to unfetter us. Freed from a punitive, unimaginative accountability regime you will see our creative professionalism unleashed.”

The Department for Education and Skills did not immediately respond to Mr Brookes’ speech.