I feel the need to try this out on yourselves as I'm struggling to get any ticket site to get the itinerary/ticket that I feel is probably best for me. I'm thinking in terms of a Super Off-Peak Return Basingstoke to Sheffield leaving on the 07.24 tomorrow to Waterloo (slow, I know but seat guaranteed). Tube to Baker Street (on the ticket) collect an item there. Tube to St Pancras (Oyster). Catch 10.32 to Sheffield arrive 12.43. Taxi to Barnsley (cash!) and back. Return to London from Sheffield starting around 15.00. Straight to Waterloo from St Pancras. Hope to get home before the trains pack up.
If it goes pear- shaped in Yorkshire I can deal with that, staying overnight and getting a morning train south.
Edit: typos
If it goes pear- shaped in Yorkshire I can deal with that, staying overnight and getting a morning train south.
Edit: typos