wedotv

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
275	everywhere it is carried	LTV (Local)	DVB-T	Text service	on some transmitters only

On LTV (Local)

44 transmitters radiate LTV [V] — a small number of sites. By nation: England (34), Scotland (6), Wales (3), Northern Ireland (1). It is operated by Comux / local operators.

Every transmitter Ofcom publish as radiating LTV.
Transmitter	Nation	Channel	ERP
Angus	Scotland	C34	1.0 kW
Beecroft Hill	England	C39	20 W
Belmont	England	C32	10.0 kW
Bilbrough	England	C42	8.0 kW
Black Hill	Scotland	C30	10.0 kW
Bluebell Hill	England	C21	1.0 kW
Brierley Hill	England	C33	200 W
Bristol Ilchester Crescent	England	C37	20 W
Bristol Kings Weston	England	C31	20 W
Caldbeck	England	C33, C29	5.0 kW
Craigkelly	Scotland	C32	5.0 kW
Croydon	England	C35	4.0 kW
Crystal Palace	England	C35	34.0 kW
Darvel	Scotland	C31	1.0 kW
Divis	Northern Ireland	C36	10.0 kW
Durris	Scotland	C41	10.0 kW
Emley Moor	England	C39	5.0 kW
Fenham	England	C36	10 W
Grenoside	England	C31	1.0 kW
Guildford	England	C33	500 W
Hannington	England	C32, C34	20.0 kW
Hemel Hempstead	England	C34	200 W
Kilvey Hill	Wales	C34	200 W
Madingley	England	C35	3.2 kW
Mendip	England	C30	5.0 kW
Moel y Parc	Wales	C27	2.5 kW
Nottingham	England	C44	100 W
Odiham	England	C27	4.0 kW
Olivers Mount	England	C39	600 W
Oxford	England	C22, C46	10.0 kW
Pontop Pike	England	C30, C33	7.4 kW
Reigate	England	C35	100 W
Rowridge	England	C37	10.0 kW
Salisbury	England	C23	200 W
Sheffield	England	C35	400 W
Storeton	England	C43	60 W
Sutton Coldfield	England	C48, C36	15.8 kW
Tacolneston	England	C32	10.0 kW
Tay Bridge	Scotland	C32	10 W
Tunbridge Wells	England	C39	400 W
Waltham	England	C41	2.0 kW
Wenvoe	Wales	C37	10.0 kW
Whitehawk Hill	England	C40	400 W
Winter Hill	England	C21, C24, C40	4.0 kW

If this is missing, so is everything here

43 other services share LTV. 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.

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