POLICE yesterday issued an unreserved apology to the mother of missing schoolgirl Tia Sharp, blaming "human error" for the delay in finding a body in her grandmother's house.

Human remains were not discovered until police conducted a fourth search of the home of the 12-year-old's grandmother, it emerged yesterday, a full week after Tia was reported missing.

In another dramatic twist in the case, Tia's grandmother Christine Sharp, 46, was arrested yesterday on suspicion of murder. Her partner Stuart Hazell, 37, who also lived in the property, was arrested on Friday night on suspicion of murder.

Sharp's neighbour Paul Meehan, 39, was also taken into custody yesterday after being arrested on suspicion of assisting an offender.

The delay in the discovery of the body in the house in New Addington, near Croydon, south London, had led to accusations Scotland Yard had blundered the investigation.

Metropolitan Police South East London Area Commander Neil Basu yesterday admitted a full search of the house last Sunday, which included the area where the body was found five days later, should have been more thorough.

"An early review has been conducted and it is now clear that human error delayed the discovery of the body within the house," he said.

"We have apologised to Tia's mother that our procedures did not lead to the discovery of the body on this search."

Basu said the first examination of the property on Friday, August 2, was not a full search.

He said mistakes were made on the second search two days later, an exercise which took two hours and was carried out in the presence of the occupiers.

"All parts of the premises were searched including the location where a body was discovered, five days later, on Friday, August 10," he said.

Basu said a third visit took place last Wednesday. This was not a search but involved the use of a body recovery dog to assist the investigation team.

"It is not appropriate to comment further on aspects of the criminal investigation currently being conducted but our investigation was such that it was decided that a further intrusive search needed to be undertaken – it was that search which resulted in the discovery," he said.

"On behalf of the Metropolitan Police I apologise for the distress and concern this delay will have caused. A continuing review and examination of our search processes will be undertaken to ensure such a failing is not repeated."

Police reportedly removed the body, which is yet to be formally identified, from the terraced house late on Friday night after Hazell was taken into custody. A post-mortem examination is expected to take place in the coming days.

It has not been revealed where the body was discovered, but officers were seen taking a ladder into the property on Friday afternoon, sparking rumours that it may have been in the loft.

Questions have also been raised over how Hazell, who had been questioned by police as a witness, managed to go missing around the time of the discovery of the body.

A huge manhunt was subsequently launched to find him, with the public warned not to approach him.

He was arrested in a public place, believed to be a park, in the south London borough of Merton at about 8.25pm on Friday.

It is understood he was identified by schoolgirl Chloe Bird, 11, shortly after he bought alcohol in an off-licence.

Her stepfather Nick Keeley, 40, said she came back home and told him that she had spotted Hazell.

He said: "The police were here within five minutes. I hadn't even finished telling them where he was, and they were here."

"There were like five cars within five minutes and then the whole area was swarmed with police."

Neighbours in New Addington yesterday spoke of their frustration at the police handling of the case after they had spent days helping in the search for Tia.

Dale Robertson, 44, said: "There's a mixture of anger and heartbreak. People feel aggrieved. They were duped. Even people who couldn't get out on the searches have posted up on Facebook that they are angry and they were duped."

Robertson said thorough searches of the house should have been done sooner. He added: "After 24 hours they should have been ripping that house apart."