OXFORD University has been told to provide more information about a key assessment of the controversial Castle Mill student flats after claims it contained “omissions”.

The buildings, built in Roger Dudman Way in 2013, have been criticised by campaigners, who said they blight views of Oxford from Port Meadow.

Last year the university produced a voluntary environmental impact assessment (EIA), which set out three options to reduce the visual impact of the flats.

It set out three options ranging from screening and cladding to removing a floor from the buildings.

Campaigners demanded the top floor be removed from six of the eight buildings.

But the university rejected that option – which it said would cost £30m – in favour of option one; a change of the colour, texture and cladding of the flats, and tree screening.

The city council hired SLR Consulting to examine the EIA and the firm has claimed other options were not explored enough.

The company’s 86-page report said the university’s conclusion had “omissions” and was “confusing”.

The council has now asked the university to provide more robust evidence about the cost of each option and why the other two were not explored fully.

Yesterday a university spokesman said: “We are committed to providing the city council with all the necessary information.”

It came after the university earlier this month said it intended to press ahead with option one of the EIA.

The decision followed a meeting of its Congregation – the university’s parliament – in February, when dons threw out a bid to have the top floors removed.

It went to a postal vote afterwards, but that was also defeated.