Dirty bomb strike is possible

Although a "dirty bomb" would cause a huge spread of radioactivity, the blast itself would not be nuclear.

A dirty bomb is essentially a conventional explosive device - not unlike those planted by the IRA - but with radioactive material rather than nails or scrap metal packed around it.

The material could be made up of waste from a nuclear power station, medical isotopes from scrapped X-ray machines or even cobalt from a food irradiation plant. Such a device could range in size from a small suitcase to a lorry. Sourcing the materials would not be difficult in areas such as the former Soviet Union.