Nice to see the chap in the black and white photo looks like a certain "honourable member for the 18th century"
I have read about how BP was still in B&W occasionally until then depending on which studio it was in, but I think this is the first time I've actually seen any post-1970 footage in B&W. (According to the TV Studios history website, on one such edition some of the equipment in said studio blew up, and that studio was never used again- I wonder if it was this episode?).
The BBC Archive channel do post some local news and Nationwide footage from as late as 1974 in B&W from time to time, and there were some B&W OBs in both 1974 elections, does almost seem odd things were in B&W that late, though it is still how most people at the time would have been watching.
When I went to the 50th anniversary event at BAFTA back in 2008, they showed a clip from one of the black and white episodes in 1974 - but it was quite an interesting clip because they said that although the studio was only able to broadcast in black and white, they could still show all the films in colour.
Richard Marson's Blue Peter: Inside The Archive, which lists the archive status of every episode of Blue Peter, denotes a couple of episodes in black and white in 1974 - 7th, 18th and 25th February were all in black and white, although it doesn't say 11th February is, but seemingly it was. Then there's a rather ragged end to the series as 23rd May comes from the Doctor Who set because of a strike (that's on a couple of Doctor Who DVDs), 13th and 24th June are in black and white (Marson assumes it was TC5, which wasn't colourised until much later than the other studios as it was mostly used for schools programmes at the time), one of which is the episode they showed at BAFTA, and 27th June was cancelled.
Seemingly the February episodes might have been a combination of the three day week and the upcoming election, while the May and June ones were affected by a lengthy BBC dispute around that time. That strike also had an impact on Top of the Pops, as there was one episode around that time when Cockney Rebel all played guitars as the scene-shifters wouldn't take any other instruments on stage and Showaddywaddy performed on the Morecambe and Wise set, and then saw it off air for several weeks.
Unfortunately, I can't find one that matches the description on TV Studio History, despite wondering about it since I read that, Marson doesn't make any reference to it. As you suggest, the story is that they had to use a studio at Lime Grove that hadn't been used for several years, only for the equipment to keel over during the show. I do know that the scene-shifters' strike in 1984 and the asbestos scare at TV Centre in 1988 meant they did a few episodes of Blue Peter from Lime Grove, which would have been a very unusual use of the studios in that period for a general show as in the eighties they were used otherwise exclusively for news and current affairs. Be like doing it from NBH these days.
This Ghanaian news presenter reading the football results is incredible pic.twitter.com/MjCH7Syw0b— Taffin (@Ballymoran) November 17, 2020
It's actually a sketch by a Ghanaian comedian, its not a real news bulletin.
He then reads Seria A and it enters a parallel universe pic.twitter.com/fpP6lr6e8L— Taffin (@Ballymoran) November 17, 2020
Attention: For those of you who are interested in those calm and professional voices that guide us around the BBC TV schedules... I've managed to get hold of next weeks Rota (from...er... 27 years ago...) So you can see who was on each channel, in Feb 1994!#Continuity #OldSkool pic.twitter.com/XL40DyQFTy— reg sanders (@regsanders) February 24, 2021
Well that's the first time a track I've put on YouTube has been tweeted by its composer.
In hindsight a period appropriate BBC style should have been used but I think I was being lazy when I uploaded it.