I'm in the UK too; just now I searched TuneIn for BBC podcasts and got a list, one of which was headed 'Genres'. When I clicked that, I got a table of categories - science, humour, storytelling and so on - and from there, clicking 'science' brought up Monkey Cage, The Anthill, RIscience, amongst others (including some sci fi!) but only as single episodes. I couldn't find a way to access a podcast series and I'd be very surprised if I could get them played on Echo just because my previous experience showed how difficult that was. TuneIn needs tuning up, I think!