Ports have been ordered to tighten security amid fears they could be open targets for terrorists.

The Government has called for tougher controls at international ports, including Newhaven and Shoreham, as part of a national initiative to prevent a terror attack on the UK transport system.

Newhaven has come under intense scrutiny in recent years following the decision to withdraw full-time Customs officers.

Critics said the move had left the port open as a back door for drugs barons, illegal immigrants and smugglers.

The Government is ordering all ports which handle ships of more than 500 tons to ensure areas can be sealed off and security staff are on 24-hour duty. The rules come in on July 1.

At Shoreham, work has begun to install new gates at the Basin Road South entrance.

The gates will still remain open to allow for lorry movements but port authorities will be prepared to close them in an emergency.

Other measures will be introduced and fencing improved where necessary.

Newhaven, owned by Newhaven Port and Properties with investment from the Seine Maritime region of France, will also have to install more gates and employ more security staff.

Full-time Customs staff were withdrawn from Newhaven at the beginning of this year, sparking protests from Lewes MP Norman Baker who said the port had become the "leakiest" on the South Coast.

Customs staff still make spot checks at the port but this is only available for 20 per cent of the time.

Mr Baker welcomed the new measures but said staff should be on duty for all sailings.

He said: "Scanning equipment is now available which can detect all weapons and instruments that can be used in a terrorist attack.

"It will be used for 100 per cent of the time at Dover, which is fully staffed 24 hours a day by Customs but only 20 per cent of the time at Newhaven.

"If I was a smuggler or an illegal immigrant, I know which port I would try to enter the country through."

Colin Crookshank, Harbour Master at Shoreham, said: "We are required to have a plan in place that allows us to respond to any changes in security levels from normal to exceptional."

A spokeswoman for the Department of Transport said: "All ports which have passenger cargo ships berthing of more than 500 tons will have to produce detailed security plans and adhere to this International Ship and Port Facility Security Code."