When trucks have been taking shipping containers out of US port terminals over the past year, they have often faced a last check. They drive between a pair of cream-coloured plastic batons containing radiation-detection equipment.
They are intended to ensure terrorists do not use one of the millions of shipping containers that enter the US every year to bring in a bomb packed with radioactive material. The detectors are an example of the millions of dollars' worth of extra security measures the US has introduced at ports following the September 11 2001 attacks.
The detectors are an added measure on top of the stringent requirements of the International Maritime Org-anisation's International Ship and Port Security Code, a worldwide measure drawn up in response to the attacks on the US, which came into force in July last year.
The UK's maritime industry - which handles 90 per cent of UK trade - now faces the question of whether it will also be forced to introduce such extra measures following the July 7 and July 21 attacks in London.
The two countries that provide most flags for international shipping - Panama and Liberia - have since July 7 both reclassified the UK as a level two security risk, instead of the more normal level one. Level two precautions are taken in ports where there is a heightened risk of a security incident.
However, industry managers say so far little has changed in the security precautions taken at ports. "I don't have any specific information about any security changes that have taken place in the last few weeks," says Michael Parker, chairman of the UK arm of Marseilles-based CMA-CGM, one of the world's largest container carriers.
Security at all ports was, nevertheless, significantly tightened last year with the introduction of the ISPS code, Mr Parker says. The code requires ports to create a firm, secure perimeter for their sites, check the identity of visitors and to create clear security procedures.
Dominic Armstrong, head of research and intelligence for Aegis Defence Services, a risk-analysis company, says the key question may be what kind of risk ports face.
The US measures have been aimed at the risk maritime containers could be used as a conduit to bring in dangerous material. The risk in the UK, Mr Armstrong says, is that bombers might target ports themselves to cause economic disruption.
He points out that al-Qaeda has already shown an interest in attacking strategic merchant shipping targets. A small boat filled with explosives was used to bomb Limburg, the French crude oil tanker, off Yemen in the run-up to the Iraq war in October 2002. "We have now seen and understand that they have an economic targeting agenda and that obviously people at the principal transport hubs have always proved effective targeting for the Islamist groups," Mr Armstrong says. "They understand very well the importance of strategic national infrastructure."
Yet equipment of the type installed in US ports is unlikely to be much help in combating attacks with conventional explosives aimed at disrupting operations.
Neil Davidson, at Drewry Shipping Consultants, says vigilance at ports has been considerably boosted by the ISPS rules. It is no longer possible to enter ports un-challenged and board ships.
Mr Armstrong says the most important step is to increase port workers' awareness of security. "The key ports already have some very sophisticated equipment installed. Spending more money on a very narrow spectrum of the threat is not the answer."