The skies above Peterborough were heavy with a blanket of thick smoke last Monday after the fire broke out in King's Dyke.

Much of one Abbey Produce-owned building was destroyed, while a neighbouring unit suffered superficial scorching.

A Cambridgeshire Fire and Rescue spokeswoman said today that careful demolition work was still continuing, but there were still some areas deep inside the warehouse which were smouldering.

She said: "There are still one or two hotspots, but we are going back to regularly monitor the situation.

"Yesterday, we started the fire investigation. It was the first time they could safely get on the site."

Police and insurers will be carrying out their own investigations, but they will also be liaising with the fire service.

The process is likely to be complex, and the spokeswoman said it was difficult to say when it would be complete.

A Cambridgeshire police spokeswoman added: "Because it's such a large-scale investigation, we are assisting the fire service."

She said if it emerged the cause was suspicious, then police would step in and play a more major role.

A spokeswoman for Brosch Direct, which rents the fire-ravaged building from Abbey Produce, said: "It's still under investigation. We are very sorry that there was a fire, and would like to thank all our employees for their support, as well as the emergency services.

"Business is carrying on as normal because we have a number of other depots."

Special report: Whittlesey factory fire, February 2008.