On 8th June, the House of Commons Library produced a briefing paper ahead of the 2nd Reading of the Bill in the Commons on 11th June. The Bill follows the Government’s reviews of its counter-terrorism strategy and of counter terrorism legislation. Part 1 of the Bill would bring in the legislative changes arising from those reviews. Part 2 of the Bill is in response to the poisoning of Sergei and Yulia Skripal in Salisbury with a nerve agent. Clause 20 of, and Schedule 3 to the Bill, would bring in powers to stop, question, search and detain people at ports and borders to determine whether they appear to be (or have been) engaged in hostile activity.
https://researchbriefings.parliament.uk/ResearchBriefing/Summary/CBP-8332