If the boss is proposing to cease employing your partner on one day, but set up a contract with him on a self-employed contract the next, this is a complete non-starter.
Employers/employees don't have a choice in the matter - HMRC have a series of tests about self-employment, and doing what is proposed will surely fail several of the tests.
See here (read down a bit).
http://www.hmrc.gov.u...ment-status/index.htm
Secondly, since his contract is effectively being terminated against his will and yet it isn't a redundancy, it is going to be difficult to see that this could be anything other than unfair dismissal. If your partner feels threatened by this (and he doesn't want to do it), he should merely say that he considers that the dismissal would be unfair and would seek redress through an Employment Tribunal. That should make the boss sit up a bit. No doubt ACAS will say much the same.
The law on redundancy (in terms of the rights of the individal) are much the same whether one person is affected or several thousand - so I really don't know what Dot is talking about (the timing of the consultation is more fixed when the numbers are bigger).