Difficult question to answer really.
I suppose you have to think about the things that could go wrong and how much you would need to fix them. So far as redundancy goes, well I don't figure that scenario into my savings equations to be honest. I have been made redundant and have left a job without another to go to and have found work quickly and easily. It maybe a different issue for you - could you, if necessary, survive with one of you on min wage for a time?
It's the other stuff I figure for. If my car has a big breakdown, I need repairs at home, if my washing machine, fridge freezer and cooker all go kaput, how much would I need to be able to sort things out quickly?
A lot depends on your financial situation as it stands. Would your bank grant you an overdraft if you suddenly needed £500?
I would say, keep at least £1k available somewhere for emergencies. Save little and regularly in another location less accessible. If you set up savings to go straight out of your bank account on a standing order in no time at all you won't miss it. I treat these as if they were bills going out.
*It is not necessary to understand things in order to argue about them. -- Pierre De Beaumarchais