Companies sometimes have some sort of restriction/policy where they won't hire people they have made redundant into perm roles within a given time period. It's not prohibited by law (afaik) but they want to avoid potential legal disputes down the line like maybe someone else was made redundant at the same time and felt they weren't given the same opportunity or whatever. What you tend to see is people get made redundant then come back as a contractor rather than an employee.Forgive ignorance here, but can't you take the redundancy cash (as compensation for loss of your current role), and then get re-employed on either of the roles they have offered you? So that way you get both - the cash gives you a safety net and the new job gives you some income while you look for something else.
Its no loss to the company - they would have to re-hire the two roles anyway if they paid you the cash and so they are no better or worse off either way.
It sounds like the redundancy package is worth about £6-6.5k(?) after tax which isn't that great, you'd take home more than that from 3 months in the £35k job.
For me the real key question would be do you think you can land a decent job elsewhere paying a proper wage within a reasonable timeframe, if you're confident in that then I'd say take the money. The beauty is you can commence your job search whilst serving your notice period and are entitled to take up to two days a week off for interviews on full pay (appreciate this could impact your commission) once you are served notice of redundancy. So it's not like you have to take the money and then sit burning it unemployed whilst trying to land the new job, if you're lucky you might lineup the new job before your last day and just walk out the door with a big pay cheque and then straight into the new job the next day.