When buying a house do buyers need to show proof of a deposit to their solicitor?

We have sold out home and we are ready to exchange ready to move into our new home, our buyer came and measured white goods today and when I told him that it looked like we were close to moving day he told me that he was getting his first time buyers ISA sorted. Now after talking to my solicitor he said it should only take 24 hours. I now have serious concerns that our buyer is not ready with the deposit? Would he have needed to show evidence of a deposit at any stage be it to the mortgage lender or his solicitor? He didn t seem to have any excitement or enthusiasm with be close to completing after waiting 2 and a half months. (Maybe I m just too excited)

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