The man was hidden in the truck which was carrying missile parts from France. He was seized by military police when he jumped out at HMS Nelson in the southern English city of Portsmouth, The Sun newspaper said.

The man, thought to be a Syrian, is believed to have crept into the vehicle in France before arriving at the site within yards of warships, including the aircraft carrier Invincible, it reported.

"We can confirm that Ministry of Defence Police did apprehend a suspected illegal immigrant after he jumped from the back of a lorry in Portsmouth naval base," a ministry of defense spokesman said.

"He was transferred to the custody of the immigration service at Portomouth continental ferry port," he said.

"There will be an investigation into the incident to discover the full facts and to see whether procedures need to be improved," he said.

The spokesman said the man was caught "pretty soon after" he arrived at the base although he could not say exactly how long it was.

He played down fears about the fact that the man was stowed away with weapons parts, since they were packed away in boxes and "not a complete missile system".

It was "extremely unlikely" the man would have had any contact with any of the components while he was in the lorry, he said.