[Clean Feed]

I think the most likely thing is a transmitter that uses an off-air feed (either permanently or in RBS mode) and - perhaps aided and abetted by atmospheric conditions - it was picking up Winter Hill/Caldebck alongside the wanted BBC Scotland feed.

BBC2 NW getting into BBC2 Scotland pres is possible, there was some weird switching at a site in Carlisle where such a switching error could have happened, but I don't think it's plausible for that to be the situation here.

With switching errors, you don't usually get a mix of sources. So, as you say, inclined to rule out that. Can't imagine an RBS situation causing this either.

It sounds like a strain of co-channel interference caused by weather conditions.

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Back in 1994, a landslip at an opencast site in Lanarkshire caused a pylon to collapse. The upshot was, it took STV and C4 off air in Central Scotland for over 3 hours.

The basics were, STV was static, C4 was black and grey lines. BBC1 and BBC2 were off air, and returned in a minute. STV returned just after 6pm, initially showing films of scottish scenes with music and their logo in the corner. Eventually, a short Scotland Today was put on air, followed by a programme, and then another short Scotland Today. Both showed scenes from the landslip.

Sounds similar to an incident in Northern Ireland at the start of 1995.

An electrical fault at the main Divis transmitter on the outskirts of Belfast caused a loss of power at the site. This also resulted in a loss of feeds to the other two main transmitter sites in Northern Ireland - Brougher Mountain and Limavady.

UTV and Channel 4 were off air completely (no blue apology caption). BBC One and BBC Two switched to RBS mode, which meant viewers received BBC One Scotland and BBC Two Scotland.

In this news report, the presenter says three quarters of NI viewers lost their pictures. Not sure how accurate that was.

rewind.thetvroom.com 

Presumably, generator power kicked in at Divis for the BBC channels, which allowed an RBS arrangement to function?