Okay, I got a filled grid with everything parsed bar 26a Home, one says, this isolated bit of land - the answer is clear but the parsing eludes me (is it a homophone?)
I haven't got the instruction yet so hints are most welcome. I wondered if it might be the 3 rd letter in each clue, after Richard, but clearly not. I'm not that au fait with Richard III (although it does contain my favourite ever pun) or the Battle of Bosworth Hill so telling me the letters are thematically placed isn't much help:-(