To expand on TyroPicard's reply:
The CAA’s funding model
91. The CAA does not have monies voted to it by Parliament and must instead recover its operating costs, plus a rate of return on capital set by the Government, through charges on the aviation industry for its regulatory services and on users of UK airspace through the Eurocontrol en route charges system.
The chapter and verse may be read here at page 34.
YS