If the company undergoes an Inland Revenue audit there is a good chance that a tax charge will be levied on the payment. If he completes and annual tax return and someone at the tax office spots the disparity (i.e. pay off but still with same employer) he could be challenged personally although any final liability might still rest
with the employer depending on the exact circumstances.

I would expect there to be no hard and fast rule concerning how long it is before you can go back. If it was under a month I am sure it would set off alarm bells. If the "redundant" employee came back very soon after as a self-employed "consultant" doubtless there would be a chance that his contract would be looked into.

I think anyone examining into these scenarios from a tax point of view would look at the correspondence exchanged at the time of the redundancy, what hapened in the interim and why a decision was made to re-hire.

http://www.legalbanter.co.uk/uk-legal-legal-issues-uk/4701-employment-after-redu...