Eleven suspected illegal immigrants were in custody last night after a chase over fields which involved more than 25 police officers, dogs and the force helicopter.

At one stage, some of the group jumped into a canal to try to swim to freedom after being spotted in farm fields between Chichester and Bognor.

The incident began shortly before 1pm when Chichester-based Inspector Dick Myhill spotted a man acting suspiciously near a car parked at Colworth on the A259.

He decided to stop his car to speak to the man who then ran off across a field but was caught by the inspector.

As he walked the man back towards the car, another four men were seen running off across fields. More police units were sent to the scene after more men and a woman were also spotted trying to flee the area.

A police spokesman said: "At one stage some of the group jumped into a canal and tried to swim away. Our officers were advised not to enter the water and the group was cut off further down the canal.

"In total, 11 people of eastern European origin have been detained, including a woman who is thought to be pregnant, and we are now liaising with the Home Office immigration department."

Police have still to establish how the group arrived in the area and whether they had hidden in a vehicle delivering to farms in the area.

The spokesman said: "The group was desperate to try and escape but this was a successful operation involving a number of police units. We are determined to crack down on illegal immigrants."