Just for complete reference this is Rule 5 from the CAA website (sorry
about the poor formatting):

Rule 5 of the UK Rules of the Air 1996
Low flying
5
(1)
The prohibitions to be observed are
(a)
An aircraft shall comply with the low flying prohibitions set out in
paragraph (2)
subject to the low flying exemptions set out in paragraph (3).
(b)
Where an aircraft is flying in circumstances such that more than one
of the low
flying prohibitions apply it must fly at the greatest height required
by any of the
applicable prohibitions.
(2)
The low flying prohibitions
(a)
Failure of power unit
An aircraft shall not be flown below such height as would enable it,
in the event
of a power unit failure, to make an emergency landing without causing
danger to
persons or property on the surface.
(b)
The 500 feet rule
Except with the permission in writing of the CAA, an aircraft shall
not be flown
closer than 500 feet to any person, vessel, vehicle or structure.
(c)
The 1000 feet rule
Except with the permission in writing of the CAA, an aircraft flying
over a
congested area of a city town or settlement shall not fly below a
height of 1,000
feet above the highest fixed obstacle within a horizontal radius of
600 metres of
the aircraft.
(d)
The land clear rule
An aircraft flying over a congested area of a city town or settlement
shall not fly
below such height as will permit, in the event of a power unit
failure, the aircraft
to land clear of the congested area. Page 2

(e)
Flying over open air assemblies
Except with the permission in writing of the CAA, an aircraft shall
not fly over an
organised open-air assembly of more than 1,000 persons below:
(i)
a height of 1,000 feet, or
(ii)
such height as will permit, in the event of a power unit failure, the
aircraft
to alight clear of the assembly,
whichever is the higher.
(f)
Landing and taking off near open air assemblies
An aircraft shall not land or take-off within 1,000 metres of an
organised open-air
assembly of more than 1,000 persons, except
(i)
at an aerodrome, in accordance with procedures notified by the CAA,
or
(ii)
at a landing site other than an aerodrome, in accordance with
procedures
notified by the CAA and with the written permission of the organiser
of
the assembly.
(3)
Exemptions from the low flying prohibitions
(a)
Landing and taking off
(i)
Any aircraft shall be exempt from any low flying prohibition in so far
as it
is flying in accordance with normal aviation practice for the purpose
of
taking off from, landing at or practising approaches to landing at or
checking navigational aids or procedures at a Government or licensed
aerodrome.
(ii)
Any aircraft shall be exempt from the 500 feet rule when landing and
taking-off in accordance with normal aviation practice. Page 3

(b)
Captive balloons and kites
None of the low flying prohibitions shall apply to any captive balloon
or kite.
(c)
Special VFR clearance and notified routes
Any aircraft shall be exempt from the 1000 feet rule when flying on a
special
VFR flight, or when operating in accordance with the procedures
notified for the
route being flown; provided that when flying in accordance with this
exemption
landings may not be made at other than a licensed or Government
aerodrome,
unless the permission of the CAA has been obtained.
(d)
Balloons and helicopters over congested areas
(i)
A balloon shall be exempt from the 1000 feet rule when landing because
it is becalmed.
(ii)
Any helicopter flying shall be exempt from the land clear rule.
(e)
Police air operator's certificate
Any aircraft flying in accordance with the terms of a police air
operator's
certificate shall be exempt from the 500 feet rule, the 1000 feet
rule, the
prohibition on flying over open air assemblies and the prohibition on
landing and
taking off near open air assemblies.
(f)
Flying displays etc
An aircraft taking part in a flying display, air race or contest shall
be exempt from
the 500 feet rule when within a horizontal distance of 1,000 metres of
the
gathering of persons assembled to witness the event.
(g)
Glider hill soaring
A glider when hill-soaring shall be exempt from the 500 feet rule.