Militant groups could one day try to hit London with a ballistic missile, a defense expert has warned.

Missiles fired from abroad would allow terrorists to beat tight security inside Britain and the government should stop thinking of the missile threat as a purely military problem, The Telegraph reported.

Peter Roberts, a senior researcher at the Royal United Services Institute think tank, said the capital would be a target for groups planning a spectacular propaganda attack or to wreak economic disruption.

He told a missile defense conference at the institute that Britain had focused too heavily on protecting its military targets overseas, rather than civilian targets in the UK.

He said: “We are not looking at adversaries who are planning to attack deployed forces.

“We are not looking at adversaries who are planning to engage in a decisive battle, we are not looking at adversaries who are going to fight by our rules.

“Our enemy is not looking to destroy our forces, they are looking for a cognitive impact. They are looking for economic disruption. They are looking to gain influence over the general population.

“London is attractive because it is so well defended there is no other way to hit it. The number of operations that the security services and the police unpick and overturn every year makes it a very difficult target.

“You only need to look at Brussels to understand that terrorists are much more fluid than we are. They will change their doctrine, their methods and their targets. Paris became too difficult, so they attacked Brussels. London is a difficult target for a conventional suicide bomber. It’s not so difficult for a ballistic missile.”