The Association of Chief Police Officers (ACPO) has launched a national campaign urging people to call a free anti-terrorist hotline to report suspicious behaviour.

In 2007, five men were sentenced to life in prison after being found guilty of planning to bomb British locations, including Bluewater shopping centre here in Kent.

It was members of the public alerting police to a large amount of ammonium nitrate at a storage unit in west London that exposed the plot.

Kent Police's Assistant Chief Constable Gary Beautridge said: "Please don't rely on others to make that call because it could be your piece of information that is the final piece needed to complete an investigation.

"This was demonstrated in the Bluewater bomb plot case where members of the public tipped police off about the offenders' suspicious behaviour. Your call could save lives.

"There will be posters and leaflets displaying the hotline number distributed throughout the county by our neighbourhood policing teams, as well as radio adverts running on local radio.

"We hope people don't rely on others but trust their instincts and report any suspicious behaviour."

Suspicious activity can include:

• Someone owning a large number of mobile phones or passports;

• People behaving differently or taking an interest in security, such as CCTV cameras without good reason;

• Someone buying or storing large volumes of chemicals for no obvious reason, or travelling for long periods of time while remaining vague about their destination.

Information given through the hotline is treated as confidential and you do not have to give your name. The number to call is 0800 789321.

You should diall 999 in an emergency or life-threatening situation.

The campaign has not been launched in response to a specific threat of terrorism.