As far as I can work out there are a number of Officers at various grades involved with Bleriot's landing at Dover.
Mr Camburn was the Preventive Officer first on the scene who interviewed Bleriot and issued him with a quarantine certificate, thus setting a precedent by treating the aircraft as a yacht/vessel and the pilot as master and owner. Also present was J.M. Johnson.
The Preventive Officers reported up the chain to the Surveyor of Dover Customs who then reported to the Collector of Dover Customs, a Mr Williams. The Collector in turn reported to the London based Board of Customs Commissioners on the 25th July that Bleriot had landed two miles from the Customs watch house at 05:00 that morning after having taken 33 minutes in crossing from France. The Collector commented that at 06:30 he had visited the scene and engaged a bystander in conversation about the future usefulness of aircraft, as a result of this conversation the Collector suggested to his superiors that Customs may soon have to take the arrival of aircraft seriously if revenue interest were not to suffer.
If the original paperwork survives there are two possible places where it might be, either Custom House London or the Customs Museum at the Albert Dock in Liverpool. I think the best place to start a search for the documents would be by contacting the curator at Liverpool.