Image copyright Getty Images Image caption The National Barrier Asset deployed in Newport for a Nato summit

UK Immigration Minister James Brokenshire has said the "National Barrier Asset" will be deployed to the French end of the Eurotunnel to prevent illegal immigration. What is the "asset"?

The National Barrier Asset (NBA) is a collection of temporary security barriers established in 2004 to provide police with the ability "to protect high profile locations or temporary events, such as party political conferences, from vehicle borne suicide attacks". It has since been used for everything from Nato summits to the London Olympics.

In short, it's a large modular fence - about 9ft high (2.7m) - that can be assembled quickly.

Now it is being sent to Calais to try to quell attempts by migrants to cross the English Channel, often in the back of lorries.

The answer It's a 9ft (2.7m) high modular fence owned by the state

Built to withstand a 7.5 tonne vehicle travelling at 50mph

Lee Doddridge, a former board member for the National Barrier Asset who now runs Covenant, a security consultancy, says it is is the first use of the asset outside the UK.

The barrier is owned by the government but transported round the UK by a contractor, whose identity is not revealed for security reasons. Sussex Police manage and store the National Barrier Asset on behalf of the Home Office. It is designed to meet the government's PAS 68 specifications - and therefore able to withstand an impact from a 7.5-tonne vehicle travelling at 50mph.

"The place you'd have seen it most is outside the Palace of Westminster," says Doddridge. It's a collection of different barrier elements, including archways, which can be deployed at short notice.

The Home Office will not disclose where the NBA is stored for security reasons. Doddridge does say that it's possible to deploy it to central London within three to four hours - including loading and unloading.

Image copyright Getty Images Image caption The fence is modular and gates can be put in

A Home Office spokesperson said that around 4km of fencing - not the whole length, which is unknown - would be sent to Coquelles. "The asset is always continually growing," Doddridge explains. The size of it has increased significantly since 2004 - it had already trebled in length by 2008.

The fact that the barrier is designed to keep out terrorists might be seen as showing how seriously the government takes the migrant crisis.

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