I have from time to time said to people that soap operas, as in the 52 weeks a year, 2 to 5 times a week variety are always set in the here and now when in principle they need not be. In particular it is possible to imagine
a) a soap opera set in the past. It is not clear to me that the incremental cost should be very great. Most of the labour and equipment costs are going to be the same, and surely once you have built the sets it is not going to be that much more expensive to have an 1890s pub or corner-shop than contemporary ones.
Aesthetically pleasing dates to start this would seem to be
i) Queen Victoria's golden jubilee
ii) Queen Victoria's death / funeral
iii) Armistice at the end of WW1
or moving further back in time, a soap set in the Globe Theatre - the Beeb could probably negotiate days / weeks to shoot scenes needing the whole theatre rather than smaller sets.
b) a soap set in a parallel time-line. You may remember 'An Englishman's Castle', set in a Britain that lost WW2. Why not have this as a soap? It would fit in nicely with the British total obsession with WW2 and the Nazis, but there are other possibilities and with a few decent props a decent steam-punk parallel world and aesthetic could rule. Maybe in the world of The Napoleon of Notting Hill, or NoNH with the serial number filed off.
c) moving on into the realms of SF, why not a soap set in a world under alien domination? Too high a level of devastation / oppression would be depressing and awkward to produce the normal 'boy meets girl, alien eats girl, alien anally probes boy' story lines, but some decent level of oppression combined with characters in the heroic human resistance would, I think, work.
As far as an approach goes, possible role models are
i) Barney Miller. This was an American comedy set in an American police station. Most of the action took place in the police-station - effectively it was a stage set with characters coming and going.
ii) The Big Time by Fritz Leiber (and one of the short stories in Changewars, similarly). Again, the action takes place in somewhere 'outside time' or travelling through time (with history changing in the Changewar story) but does not leave the set.
I did actually think that this approach could work for something based on The Atrocity Archives by Stross, what I think of as 'Barney Miller with tentacles'.
However, the idea that stands out is....
... daily Torchwood
Over to you Russell!