Replacing the radar system at Norwich International Airport - which bosses say is needed to stop cars on the Norwich Northern Distributor Road from interfering with air traffic control - is to cost taxpayers some half a million pounds more than originally thought.

It emerged last summer that the airport and Norfolk County Council were in negotiations over the effect the 19.5km road, which will stretch from the A47 at Postwick to the A1067 Fakenham Road, will have on the radar system.

Airport bosses said the traffic on the £148.5m road would show up on the airport's radar system, interfering with the safe arrival and departure of planes from it.

County Hall officers said, unless a solution to that problem could be found, the airport would have to object to the road, despite having long supported the economic benefits the NDR has been touted as bringing.

The solution the council came up with was to contribute £1.3m over eight years towards a replacement system. The council would actually provide the financing for the total cost of the radar replacement with the paying back the total cost over the next two decades.

But, at a meeting of the controlling Labour/Liberal Democrat cabinet yesterday, it emerged the cost had increased.

A report which came before the cabinet stated: 'As a result of recent changes in the radar market, costs for the radar hardware systems have increased notably and the lowest cost solution from the preferred bidder is in excess of that originally set out when the decision to provide a funding package was previously made by cabinet.'

The report explained that the price tag hike means the council will need to pay an extra £576,000 - taking its total to just under £1.9m. The airport will bear the rest of the costs.

However, council officers said the extra cost had been 'off-set by savings elsewhere on the project' and the overall cost remained at £148.5m.

This summer will see a six-month examination of the proposal for the road by a planning inspector or a panel of planning inspectors, with a decision on whether the road can go ahead due next year.

• What do you think of the NDR? Write, giving full contact details, to Letters Editor, Prospect House, Rouen Road, Norwich NR1 1RE.