Coke 611 For the smaller UK airfields that are not "customs" airfields, many have made arrangements so that you do not have to book customs in advance. This concession only applies to G reg aircraft, with only EU passport holders on board, flying to a destination within the EU.
It is worth asking your flying club, or airfield operator about your local arrangements. For instance at Elstree, all we have to do is fill in a customs form & hand it into the tower, with the flight plan. The FISO then faxes the form to the local customs office. On the form you have to enter your ETA back at Elstree. In practice customs officers do turn up at Elstree occasionally, to do the odd spot check on returning aircraft.