Christ
quite a lot here
https://www.icsa.org.uk/knowledge/governance-and-compliance/analysis/gagging-clauses-protected-disclosures
if you kiss and tell tale amounts to a protected disclosure
you can make it even tho you have signed and taken the moolah
I thought it was straightforward that the judges of the High Court ( bless all of them!) would find it not in the public interest that contracts were concluded to prevent criminals coming to justice - and hence voidable and unenforceable
but they didnt
( just in case you are wondering a corrupt contract such as a contract for prostitution will NOT be enforced, and concluding a contract to pay for the return of stolen goods is a crime innit? let alone void and unenforceable at common law]