In reply to The New NickB:
> To be honest, the living apart bit isn't what I found odd, there are lots of reasons for that.
in fairness without asking a lot more about the relationship you're being a bit judgemental to suggest it's odd.
op -
lots of letting agents do this now. It's ridiculous and a lot of people can struggle if they're in an area with few agencies and they all play the same game - I know while my mum would be happy to give me a loan if I asked (I don't though that's not relevant) she would be paranoid about being a guarantor and refuse. The guarantor needs to own a house generally so while I don't know for sure the legality about it, there's the suggestion that if your partner defaulted and you couldn't pay then the agency could cause you to lose the house, so that puts people off even in 'completely safe' situations.
Anyway, if there's lots of choice and she's not in a mega rush I would suggest looking for an agency that doesn't do this (or it could be the landlord that is insisting - ask) as those deals also tend to come with overly high fees and generally arsey contracts (monthly visits, sign saying you will clean the shower head out in a specific way once a week, bollocks like that) as well as simply the complication of the guarantor bit. Also handing over 6 months rent then finding out there's something terribly wrong with the house - it's a lot easier to avoid paying rent when you're in that situation than trying to get it back.
If this place is perfect or she really needs to get in quick then it should essentially be the cost of rent not paid up to when she leaves or when they're able to kick her out. In theory the latter could take a while if she refuses to leave. In practice - letting agencies can be pretty dodgy and flaunt the law with their contracts (things like saying admin fees are non refundable should they choose to not give you the house - it's only non refundable if you pull out or you claim something that isn't true on your application) so they could be trying to make the guarantor responsible for all sorts - including unlimited amount of repairs to the house if it's left in a state (or it's already got problems that they try to blame on your partner). While that may not be legal (I've not looked into that specifically) it can be very difficult to deal with a situation where bailiffs are knocking on your door and the letting agency won't communicate with you.
So my advice generally if it has to be this place/deal - go get the fine print and look it over. Find any holes in it and speak to them to get them to amend the contract so they're filled (if they refuse to do so then I'd really run a mile).