HIGH levels of lethal carbon monoxide fumes have been found at a block of flats in Derby for the second time in just over a year.

Four residents at Pride Park Lodge, in Chaddesden, were taken to hospital after inhaling the poisonous gas.

Investigations are still on-going but initial tests have found high levels of the fumes coming up through the ground into the building.

The flats were hit by carbon monoxide coming up through a plughole in November 2008, resulting in a couple and their baby being hospitalised.

An investigation at that time concluded it was an isolated incident probably caused by a resident pouring chemicals or petrol down a drain.

But, at 1am on Saturday, residents were again alerted to fumes when several carbon monoxide alarms in the building started ringing.

Residents of all nine flats were evacuated and are temporarily staying with friends or family or in hotel rooms provided by the landlord.

It is not known when they will be able to return.

The highest levels of gas were found in the same flat as last time, now occupied by Tony Richardson.

The 31-year-old said he noticed a bad smell when he arrived home from work in the early hours of Saturday morning.

He said: "I was just about to go to sleep when there was a knock on my door and one of the residents told me the alarm was going off."

He felt sick and dizzy and was taken to Royal Derby Hospital, where he spent three hours before returning to the flats in Meadow Lane. He slept in his car.

He was the worst affected but three other residents were also treated in hospital and discharged on Saturday morning.

Landlord Steve Naylor said that following the 2008 incident he had done everything he could to ensure the building was safe. He said: "I had a meeting with environmental health and all the other agencies.

"There seems to be no rhyme or reason for it happening again and clearly it needs further investigation."

He said the possibility of a leaking gas main had been ruled out following a check by gas company Transco.

He described the previous belief that the fumes came from chemicals poured down a drain as "clearly wrong".

He said: "We've lifted the membrane underneath the gravel in the back garden and its coming from there, too. We think it could be landfill."

Mr Naylor said that carbon monoxide alarms had been fitted in all the flats after the previous incident but admitted they had not been regularly tested or maintained and that some had been removed by decorators.

Mr Richardson said he did not have an alarm in his flat.

Michael Kay, Derby City Council's environmental health manager, said he had been satisfied with the investigation in 2008. He said: "It indicated that it was an isolated incident. Now we need to work with Mr Naylor to get to the bottom of it."