Councillors have turned down plans for a new home after a conservation expert warned that it could wreck a project that saved the UK's rarest butterfly species.

Steve Doyle, 73, has run a marsh fritillary captive breeding programme in the garden behind his Durdar home for 13 years.

The species was on the brink of extinction in Britain when he launched the project, starting work that eventually led to the reestablishment of 18 colonies across the county.

But the project would have been wiped out had councillors approved plans for a new house next to his home because the resulting shadows would have had a devastating effect on the growth of the butterfly caterpillars.

Their cages would have lost two hours of sunlight every day as a result of shadow case by house as currently proposed, said Mr Doyle.

He said the breeding programme continues to be necessary because colonies can suffer sudden and catastrophic population crashes.

Mr Doyle's concerns were shared by Dr Keith Porter, who has also been a leading light in the battle save the marsh fritillary butterfly.

Sunshine is vital for the caterpillars if they are to thrive, and the house as currently proposed would reduce the daily dose of sunlight by two hours, said Dr Porter.

Both men said the application could be modified and the house repositioned to avoid a critical loss of sunlight.

After discussing the planning application on Friday, members of Carlisle City Council's development control committee voted by eight votes to three to turn it down.

In its planning decision notice, the council states: "The proposed development by nature of its scale, height and location will have a negative impact by means of the unacceptable loss of sunlight on a breeding programme for a nationally important UK BAP(Biodiversity Action Plan ) priority species."

A planning case officer recommended the application be approved after a local architect wrote a report saying the resulting shadow would not significantly affect Mr Doyle's garden.

In a statement before the meeting, Dr Porter said: "A key requirement of marsh fritillary caterpillars is direct sunlight.

"They depend on sunshine as a means of raising their body temperature by basking - this is a part of their natural behaviour and enables them to grow much more rapidly than simple air temperatures would suggest.

"This is a behaviour I discovered when studying this species as part of my doctoral thesis and I have published several scientific papers on this almost unique behaviour.

"Insects are usually “cold-blooded” and cannot generate their own body heat; the marsh fritillary caterpillars raise their body temperature to 37 degrees C by basking.

"If denied access to direct sunlight the caterpillars grow very slowly and fail to develop..."