To back up what FFF was saying, here's a few bits from Rule 5 in the
ANO.
(2) (a) The provision of paragraphs (1)(a)(ii) and (1)(c)(i) shall not apply to an aircraft flying: (i) on a route notified for the purposes of this rule; or (ii) on a special VFR flight; unless the aircraft is landing or taking off.
paragraph (1)(c)(i) is specific to helicopters so I'll ignore it for now.
paragraph (1)(a)(ii) states :
(ii) a height of 1500 feet above the highest fixed object within 600 metres of the aircraft:
As FFF says, there is nothing in there that exempts you from the glide clear rule which reads :
(i) such height as would enable the aircraft to alight clear of the area and without danger to persons or property on the surface, in the event of failure of a power unit and if such an aircraft is towing a banner such height shall be calculated on the basis that the banner shall not be dropped within the congested area; or
Hope that clears it all up.
Regards
Stoney X