London Evening Standard/London

Experts in chemical and biological threats were searching houses in London yesterday after two people were held under anti-terror laws.

More than 30 officers in a dozen vans raided a £650,000 home at Streatham Hill in an “intelligence-led, pre-planned operation”. A 19-year-old man was arrested at the address and neighbours witnessed police officers in masks digging in the garden and carrying out searches inside the house.

Anti-terror police mounted a similar operation at a house in Stratford. The teenager was arrested on Saturday under the Anti-terrorism, Crime and Security Act but has since been released on bail. A 36-year-old woman was held on suspicion of a similar offence at the address in Park Road, Stratford, at 4pm on Sunday.

She was interviewed at an east London police station yesterday.

Scotland Yard said there was nothing to suggest that local people were at “immediate risk” and that the protective clothing was a precautionary measure. No one was evacuated in the raids and it is not believed that the arrests were linked to an organised terrorist plot. However, officers are understood to be searching for a chemical or toxic substance after a tip-off.

Neighbours in Wyatt Park Road, Streatham Hill, told how about a dozen police vans, including a satellite communications truck, swooped on the semi-detached, four bedroom house.

Around 20 uniform and plain clothes officers entered the address while others blocked off both ends of the road for an hour-and-half, refusing to allow residents in or out of the street. The search was later widened to include a neighbouring house. Officers erected floodlights and tents in the gardens of both houses.

Neighbour Necmiye Atalay said: “They are a very quiet family. We are stunned by this. We have never had any problems with them. To have such a massive raid here is a real shock. It is just a normal suburban street. As for the other house they are searching, people come and go but there does not seem to be any connection between the people in the two properties.”

Neighbour Peter Petchey, 60, who works for a law firm, said: “They seemed like a very nice family and they must have lived there for at least 12 years. That boy’s old man is not going to be too happy.” A neighbour, who asked not to be named, said: “They are a really, really nice ordinary family, a friendly middle aged couple with three boys.”

Serena Agnello, 22, a student, said: “The police have come in to use my loo a few times and one told me they found something, but he wouldn’t say any more. They said they’re going to be here for the rest of the week, so they must still be looking for something.”