A row has blown up over the revelation that GCSE results have plunged at schools close to Middlesbrough's two controversial 'city academies'.

Critics of the academy programme warned the expensive, privately-sponsored academies "creamed off" the most able pupils from neighbouring schools - lowering their results.

But one of the academies, King's, insisted none of its pupils taking GCSEs last year had been admitted from nearby comprehensives.

The comparison of results, released to MPs, revealed falling GCSE performance in 2004 at two of the three secondaries closest to both King's and Unity City academies.

In the case of King's, the number of pupils gaining five or more A*-C grades at GCSE at Newlands Catholic School fell from 48% in 2003 to 43% last year.

St David's Roman Catholic Technology College (down from 46% to 34%) also showed a decline, although performance improved at King's Manor School (up from 31% to 37%).

Unity City is also close to both Newlands and King's Manor. At its third neighbouring school - Ormesby - there was a fall from 24% to 21% last year.

Phil Willis, Liberal Democrat education spokesman, said it was "inevitable" that city academies would attract the best pupils, because they were new and usually offered better facilities.

He added: "A shiny new £20m school, with all the glitz that Labour has attached to academies, is bound to have a knock-on effect, because aspiring parents want to send their children there.

"If an academy is built in a community without proper planning, neighbouring schools that are struggling to raise performance and struggling to attract good staff will suffer."

This week, the National Union of Teachers (NUT) passed a motion at its annual conference condemning the academy programme and demanding a halt to it.

Spokeswoman Nina Franklin said: "We have fears that academies cream off the best pupils. It is a real concern that this will have an impact on other schools in the future."

But King's Academy insisted its 2004 GCSE crop had been pupils at the two schools its replaced - Brackenhoe and Coulby Newham Schools - not at neighbouring comprehensives.

A spokeswoman said: "We don't select pupils, so we don't cream off students from other schools. Our intake is based on catchment area alone."

Nobody was available to comment at Unity City Academy, which also replaced two predecessor schools.

Last week, the Labour-dominated education committee heavily criticised the plans for 200 academies across England, because there was no firm evidence that they raised standards.

The committee's report called for no more than 50 until the scheme had been "thoroughly evaluated" - and questioned the £5bn cost.

Critics of the programme have also highlighted how the private sponsors can dictate the curriculum and appoint the governors while providing just 8% of the £25m cost.