Your employer is, of course, technically in breach of the contract between you and it, but your best course of action will depend on many factors.
I suggest you look here in the first instance and work out what situation applies to you.
http://www.direct.gov.uk/en/Employment/Employe es/Pay/DG_10026695
On that page you will find a link to another page about temporary lay off and I suggest you look there as well.
If there are no clauses in your contract of employment about lay-off arrangements or none are known to apply generally to the whole of your industry sector, then none apply. I think you would know if such arrangements applied in your case so there probably none.
If the company went belly-up, you would not lose your right to statutory redundancy - you would merely claim it from the Government. However you need to factor this against not being paid for the next 3 months. Personally I think the employer is making ridiculous demands and the company should be pushed into insolvency. If the company went belly-up in September, whilst you and other employees owed wages would be top of the list of creditors, you cannot guarantee that you would get your back-pay - I do not believe that the Government redundancy fund would pay your back-pay - only your statutory redundancy.
So you need to factor of of that against your 'expectation' of bigger contractual redundancy payments that you seem to think you are hanging on for - plus the thought that things might turn around.
Personally I'd be out there looking for another job at the same time (which you are maybe doing).