@GorgeousLadyofWrestling and @Sparklyblue - so sorry to hear of your experiences and apologies to anyone that was kind enough to have responded with advice / experiences and that I haven't acknowledged because need to read through again and get brain in gear.
Thanks again to all with empathatic responses.
Update - Buyer's mortgage was reconfirmed last week and money transferred to their Solicitor.
Obviously buyer wanted to confirm completion date as soon as possible however, as much as we'd have liked to accommodate them, their Solicitor went radio silence re confirming receipt of funds and putting forward proposed exchange and completion dates; they were sitting on the money. I know it's meant to be an escrow account but takes the piss.
Also, any solicitors around to explain why completion has to be on a Friday?
In ye olde days, banks would shut at 15.30; strangely enough, this way of working seems to have carried on with reference to mortgages so if anything goes tits up, you can't get hold of anyone.
We're not going to be caught out again with exchange and completion being on same day. We lost the cost of our first removal and re-booking a slot that aligns with your requirement is difficult - they are busy with everyone trying to take advantage of temporary Stamp Duty regulation!
Big news is we've exchanged. We've always been committed our side of the bargain but their Solicitor fucked up. We've always felt sorry for buyer who had to move into expensive, temporary accommodation.
As an aside, what did you leave for your Buyers?
My DH had already sent across any legally required info (months ago) e.g. leasehold, service charge, ground rent required but he's prepared a folder and additional stuff including:
All warranties of appliances
All manuals re above
Extra halogen light bulbs
Additional rolls of feature walls', wallpaper
Bathroom tiles (ensconced under Bath - accessed through panel)
Service provider info, if they want to take on eg EE, EFG, Virgin.
A bottle of nice Champagne
We will leave flat immaculate and ready to move into.
Trying to think of anything that requires 'a knack' e.g one of my previous flat's Balcony door had to be locked / unlocked by ensuring handle was upright but can't think of anything here.
Thanks again to all with pertinent advice!