The invention relates to an access panel configured for fixing to a service aperture in a wind turbine tower wall; wherein the access panel comprises a main panel and an adjacent sub-panel; the sub-panel comprising a bearing surface at an edge thereof; the main panel comprising a reference surface at an edge thereof; the main panel and the sub-panel being abuttable along a common seam; the seam comprising a said sub-panel bearing surface abutting a main panel reference surface; the main panel being dimensioned to close a main region of a tower wall aperture whereas the sub-panel is dimensioned to close a first sub-region of the aperture. The invention includes a method according to which the sub-panel is placed into a tower wall aperture and adjusted to bring its bearing surface into a predetermined position. Thereafter, a main panel is placed in the aperture with its reference surface in abutment with the bearing surface, thereby quickly and easily and reliably locating the main panel for securely fixing in the tower aperture.