The relevant legislation in the UK is SI 2798 of 1996.
Definitions:
"accident" means an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disembarked, in which—
"(a) a person suffers a fatal or serious injury as a result of—
— being in or upon the aircraft,
— direct contact with any part of the aircraft, including parts which have become detached from the aircraft, or
— direct exposure to jet blast,
except when the injuries are from natural causes, self-inflicted or inflicted by other persons, or when the injuries are to stowaways hiding outside the areas normally available to the passengers and crew, or
(b) the aircraft sustains damage or structural failure which—
— adversely affects the structural strength, performance or flight characteristics of the aircraft, and
— would normally require major repair or replacement of the affected component,
except for engine failure or damage, when the damage is limited to the engine, its cowlings or accessories; or for damage limited to propellers, wing tips, antennas, tyres, brakes, fairings, small dents or puncture holes in the aircraft skin; or
(c) the aircraft is missing or is completely inaccessible;"
"incident" means an occurrence, other than an accident, associated with the operation of an aircraft which affects or would affect the safety of operation;
"serious incident" means an incident involving circumstances indicating that an accident nearly occurred;
Removal of damaged aircraft
7.—(1) Subject to paragraph (2) and regulation 9 below, where an accident, or a serious incident which results in the withdrawal from service of an aircraft, occurs in or over the United Kingdom no person other than an authorised person shall have access to the aircraft involved and neither the aircraft nor its contents shall, except under the authority of the Secretary of State, be removed or otherwise interfered with.
So basically, if it is an Accident or Serious incident, the aircraft can not be moved until the AAIB say so. For a simple incident, the guidance vailable from the AAIB should be followed with respect to reporting.
Regards,
DFC