In the UK the relevant thresholds are:
£10,000+: Deposits in this range, especially cash, have a high likelihood of being flagged for scrutiny.
£25,000+: Deposits of this size are almost certain to be flagged for review, and you will likely have to prove the source of the funds.
£50,000+: Large deposits may require formal source-of-funds verification.
Banks in the UK do not automatically notify HMRC about large deposits unless:
The deposit is flagged as suspicious under AML regulations.
It triggers a Suspicious Activity Report (SAR) to the National Crime Agency (NCA).
HMRC specifically requests financial data using a Financial Institution Notice (FIN)