Tempting though it must be to exaggerate the situation for effect, the 'nearly 20' people said to have been identified by UK Security Services are not 'known terrorists'. If they were then the UK has plenty of legislation on the statute books which would mean that they were not housed in hotels pending coinsideration of their asylum claims. Even the Daily Mail only describes them rather and possibly intentionally as 'suspects'.That covers a lot of possibilities.
Someone more cynical than me might be surprised that such details of national security have been leaked to the Daily Mail and note that the Daily Mail has a less than below average reputation for veracity. It might also be noted that these allegations emerged only a day or so after it was announced that The Home Office had been forced to concede that they have absolutely no evidence to suggest that the majority of asylum seekers are economic migrants, something else that we had been assured by successive Home Secretaries and right wing newspapers to be the case.