My sister has bought some jewellery. We need to keep it safe (ie not in the house).

Do banks still do this kind of thing or do we have to go elsewhere?

if you mean safe deposit boxes, a lot of banks have been phasing them out. To be honest, you're better off getting a small personal firesafe professionally fitted in the house. It'll cost you less overall (as deposit boxes are now fairly rare, the costs have gone up significantly) and if she actually wants to wear the jewellery she can, as oppose to having to think a few days ahead to go and get it.

In reality almost any precautions aren't justified by the risk unless your sister lives in an area that sees a lot of burglary. Check out how much getting it insured as a single item costs, check out how much a safe is and decide. If she puts it in a safe deposit box in all likelihood she'll never wear it because of the hassle of picking it up and what's the point of jewelley that never gets worn?

We have a small, very well hidden safe here. Nothing fancy, but it'd be a total bugger to get at. Certainly not anything you're likely to walk out with quickly, if you found it at all.
So I'd go with a good, well hidden safe in preference to leaving it somewhere else. And, as Jon says, better to have it to hand if only to admire from time to time.

Plus you can't just walk in and access your safe deposit box you have to make an appointment.