An elaborate bomb threat at a city centre office block caused traffic chaos in Brighton today.

Staff at the four-storey Lloyds TSB offices in Gloucester Place called police at 8.30am when they discovered a note saying there was a device in the building.

There were signs the building had been entered and the offices were evacuated and the area cordoned off.

Police later extended the cordon from St Peter's Church to the south end of Victoria Gardens, closing two of the city's main north-south thoroughfares.

At 11am, an Army bomb disposal team used a robot to search the area inside the building where the note had been found.

Police searched the offices, on the corner of Gloucester Place and North Road.

The all-clear came at 12.20pm and forensic officers moved in to search for evidence as the bomb disposal team left.

Chief Inspector Stuart Harrison said: "A note was found. Part of the building had been tampered with.

"As far as we were concerned it was pukka. There was a suggestion somebody had been in the building, fixed the note and obviously made preparations.

"There was something else there apart from the note. We are talking about a hoax improvised explosive device.

"A search of the building was conducted by bomb disposal teams. Evidence has been removed. We are now confident the building is secure."

Police would not comment on what was found in the building.

Chief Insp Harrison said: "There has been major disruption to the life of the community caused by traffic diversion and we have an ongoing investigation to find the perpetrators and prosecute them under the Malicious Communications Act.

City centre traffic was described as "absolute mayhem" for most of the morning.

Northbound traffic was diverted through North Laine, while vehicles travelling south went via Richmond Parade and John Street.