It is unlawful to subject a worker to detriment or dismissal because they made a protected disclosure whilst working for a previous employer.
The EAT has ruled that an individual will have a claim where he was a worker at the time he blew the whistle and because of this was subjected to detriment or dismissed when working for the same or a new employer.
In practice a new employer is perhaps most likely to discover - and take a dim view of - prior whistleblowing where the two employers are in the same group of companies or where a function has been outsourced.
Once an employer is on notice of an individual's history of whistleblowing, it will be all the more important to ensure there is a paper trail evidencing legitimate reasons for the employer's conduct (in the same way as when there is a potential discrimination angle).
The decision also highlights a gap in the law: there is no prohibition on rejecting a job applicant because of their history as a whistleblower, as individuals are only protected once their employment has started. (BP Plc v Elstone, EAT)