The idea
It is necessary to notify Special Branch when a UK light aircraft wishes to fly to or from the Channel Islands, Northern Island, ROI and the Isle of Man. Special Branch may elect to drive, usually 2 officers, to the UK departure/arrival airfield. This does not have to be done if a light aircraft wishes to fly to Europe eg France.
So if one wants to circumvent this procedure even a Year 1 schoolchild, let alone a terrorist, would find it simple. Just fly to France, land there and then fly unresticted to the Channel Islands et al.
The need to still inform Special Branch and the ensuing costs to the police is, in my opinion, an absolute waste of money.
Why is it important?
Saving police resources and costs.