schmunk
Why oh why oh why?
Not at all, it's a fairly normal clause in a termination agreement to require the (former) employee to take reasonable steps to mitigate the losses from a wrongful termination, in the same way as most other commercial contracts.Sounds like a highly improbable clause, never heard of such a thing sounds like it would be illegal.
This article from a very reputable source, whilst paywalled, gives enough of a flavour in the visible paragraphs: https://www.lexisnexis.co.uk/legal/guidance/wrongful-dismissal-mitigation