Worried police sealed off one of Sussex's busiest roads to blow up a bat box they thought was a terrorist bomb.

Sussex Police evacuated homes and shut the busy A23 at Pease Pottage over fears the machine next to the dual carriageway could be explosives.

An Army bomb team was brought in and they blew up the package - a gadget being used to check how Sussex's bats were doing.

Last night ecologists said Sussex Police had been warned the devices had been fitted in the area by the Highways Agency to test whether expanding the A-road could affect wildlife in the area.

But the force refused to go into detail about the incident - and would not even confirm what the box was.

Officers were called to Handcross at noon yesterday after a member of the public spotted the box under a bridge over the A23.

Police immediately set-up a no-go zone around the site and offered 20 residents shelter in the parish hall while the bomb disposal unit investigated.

Both lanes of the A23 at Pease Pottage, near the motorway junction, and the A272 at Bolney were closed for several hours.

The Horsham Road at Handcross was also shut and traffic diversions set up.

Drivers were advised to avoid the area because of traffic gridlock.

The £1,000 bat detector, which monitors the nocturnal creature's calls, was put under the bridge as part of a survey of the endangered creatures.

Ecologists are recording bat movements in an environmental impact study for the Highways Agency.

The agency is considering widening the carriageway at Handcross and wants to find out what effect roadworks would have on wildlife.

A Highways Agency spokesman said: "We deeply regret the inconvenience caused by today's closure of the M23/A23.

"We can confirm the object was a bat box placed on the bridge as part of an ecological survey in advance of a roads scheme.

"We are working on ways to improve identification of our property to avoid a repeat of today's incident."

Sheila Wright, the secretary of Sussex Bat Group, said: "We believe it was a bat detector and positive monitoring system which had been left in situ by a company.

"They record bat passes so ecologists know how well-used that area is by bats.

"The Highways Agency is doing a very responsible thing by holding this survey."

"They are electric devices and have a battery attached to them so they could look suspicious.

"But I would think they would have had the name and details of the manufacturer written on them.

"The devices are left in situ and are sometimes hidden to stop them being vandalised, so this might have seemed suspicious too.

"Some of the ecologists had told police that they had left some equipment so they would be aware of it in case it was stolen.

"I don't know whether the police knew about that particular device but they had been told something was in the area.

"I'm surprised the police didn't check before they over-reacted."

A spokeswoman for Sussex Police said: "As a result of a well-intentioned call by a member of the public, the package was investigated, but found to be harmless."

The spokeswoman described the package as "some form of legitimate monitoring device" and would not confirm it was a bat detector but added that it had been "disrupted" by the bomb disposal team.

The force was unable to say how many officers had to be rushed to the scene during the operation.