Channel Islands
No, this is the crazy situation. If you do it your way you are not flying from the UK to the Channel Islands. At one time, before Biggin had Customs, but not Special Branch, it was common for pilots flying from Jersey to Biggin to do as you are doing in order to avoid the cost of landing at an approved UK airfield. Incidentally, a friend of mine who sails told me some time ago that this regulation does not apply to sailing from the UK to Jersey and return.