Well I drive about 20k a year too and I've replaced nothing to date so I'm probably a good benchmark.
at around 50k you can expect to replace brake pads and tyres, there shouldn't be much else really that wears out. Clutches shouldn't go that early but can do if you had a really bad driver before.
as long as it's had a full service history everything that needs replacing should have been done, 48k service is about £500 so that should be fine.
tyres aren't cheap, the yoko Geolanders will set you back around £800 a set, that said, at 48k miles I'm still on my original tyres so they may be better value longer term that others. Worth noting these tyres were designed by Yokohama specifically for Subaru.
so in answer to your question, if they've not been done recently then I'd assume you'll need brake pads and tyres soon.