4000 terror suspects in UK

Don’t ya love how many terror suspects there are? Apparently there are 4,000 terror suspects and their sympathisers in this country. This seems to be a lot more especially seeing at the start of the month there were only 1700 terror suspects. In October 2006 the number of terror suspects was at 1500 so the numbers have almost tripled in about 9 months.

Is this scare mongering or is it real?