TV Warehouse

Logical Channel Numbers are assigned by the platform, not carried in the transmission, which is why they differ between nations and why a retune can move them.
Channel number	Where that number applies	Multiplex	System	Format	Availability
87	everywhere it is carried	GI (G-MAN)	DVB-T	16:9 SDTV	Greater Manchester only

On GI (G-MAN)

2 transmitters radiate GI [V] — a small number of sites. By nation: Wales (1), England (1). It is operated by unconfirmed.

Every transmitter Ofcom publish as radiating GI.
Transmitter	Nation	Channel	ERP
Wenvoe	Wales	C31	1.0 kW
Winter Hill	England	C27	1.0 kW

If this is missing, so is everything here

8 other services share GI. A multiplex is one 8 MHz transmission carrying all of them at once, so it arrives whole or not at all — losing exactly one of these and keeping the rest is a fault in the channel, not in your reception.

That's EntertainmentThat's 60s MCRThat's Oldies MCRThat's TV (UK) MCRThat's TV 2 MCRThat's 20th Century MCRTV Warehouse +1That's Classics

Which multiplexes should reach a particular address is the postcode lookup.