British officials have admitted that a computer system used to screen for extremists crashed briefly but deny newspaper claims that national security was compromised.

The Home Office Thursday challenged The Daily Telegraph's claim that the failure of the Semaphore computer system left Britain unable to prevent extremists from entering Britain.

"We maintained full checks on 100 percent of arriving passengers using the Warnings Index — which is completely separate to Semaphore, our pre-departure advance checking system," the statement said.

The newspaper says the failure of Semaphore in June meant that incoming passengers were not checked against electronic watch lists.

The Home Office says its "multilayered" approach to border control meant security was not weakened.