A BBC report, with the official stats on arrest etc, here is one passage:
There were 400 arrests on suspicion of terrorism-related offences in the year to the end of September 2017. That's the highest recorded figure, up more than 50% on the previous year.
The author concludes:
So 2017 was a bad year for attacks, while still nowhere near the levels of The Troubles in Northern Ireland. But it definitely looks like there has been an unprecedented level of activity around tracking down people who are suspected of wishing to do harm to others.
Link:https://www.bbc.co.uk/news/amp/uk-42420358?