Has he spoken at all (or is it in the will) about how and where he wishes to be buried or cremated?
As mentioned by a pp, is the debt documented (eg is there something, anything, in writing or was it just done on a handshake)?
"...he is owed money, about £200k. That’s about 10% of the estate."
If £200k is 10% then that suggests the total estate is around £2 million.
If an estate goes above £2 million then there are extra calculations to do. They're not difficult though and if you're capable of doing the probation yourself then you will be able to do a couple of extra calculations.
A pp said to "sell shares". That would be a mistake as that would crystallize any capital gains and so CGT would have to be paid and then it would still be subject to IHT on your uncle's death. Do not sell any assets that have increased in value before your uncle dies unless it is absolutely necessary.
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"but I think the accounts will be frozen?"
The accounts are frozen so that no more money can come out of them. If there are any ongoing payments that need to be maintained (eg gas/electricity for the house etc) then you will need to contact companies to explain the situation.
What happens then depends how much is in the account and which bank it is. For example, I bank with Barclays and they say that if all the sole accounts with them come to no more than £50k then you do not need to wait for probate.
In that situation you need an original death certificate or certified copy and proof of your ID (eg passport, driving licence etc)