When I was selling my father’s house, the whole thing ground to a halt in some sort of stalemate, and I ended up ringing the buyer’s solicitor to get her to tell me exactly which piece of paper she believed she had not received from my conveyancer (my original solicitor having gone bust shortly after being instructed!), so that I could then tell my conveyancer to supply it. After agreeing that we weren’t officially having this conversation because she wasn’t allowed to talk to me, she told me what was missing. It was a form I had filled in several months previously...
Probate? Fiddly but straightforward. HMRC IHT helpline are very helpful. HMCTS less so.