It seems to be a virus spreading amongst traffic control companies
See this thread for some details from Ranty Highwayman: https://twitter.com/lucullus/status/848156960381906944
My reading is that if a cycle lane is to be closed and there is no alternative route, there is a sign specified for this situation: 'Cyclists dismount and use footway' (traffic signs manual chap 8 pt 3 drawing P7018.1) . We're talking something along the lines of closing the cycling half of middle meadow walk. It's interesting having a skim of part one, this sign isn't ever used in an example layout.
Temporary traffic lights like these are not an appropriate use, as a cyclist is quite entitled to use the roadway.
(edit, Just noticed this is the spotted thread, any chance of a split into a new topic? It's worth discussing.)