There is no such law, and there, probably, never will be. It is just electioneering twaddle.
What there is .... since 2015 .... is the Counter-Terrorism and Security Act, which includes the responsibilities on specific bodies to have “due regard to the need to prevent people from being drawn into terrorism”.
Would you not think that that is worthwhile?
There is enough protection within the law and guidance to avoid over-reaction.
From The Counter-Terrorism and Security Act 2015 (Risk of Being Drawn into Terrorism) (Amendment and Guidance) Regulationsￂﾠ2015 (legislation.gov.uk) :
‘Safeguarding’ is the process of protecting vulnerable people, whether from crime, other forms of abuse or (in the context of this document) from being drawn into terrorist-related activity.
The current UK definition of ‘terrorism’ is given in the Terrorism Act 2000 (TACT 2000). In summary this defines terrorism as an action that endangers or causes serious violence to a person/people; causes serious damage to property; or seriously interferes or disrupts an electronic system. The use or threat must be designed to influence the government or to intimidate the public and is made for the purpose of advancing a political, religious or ideological cause.