Well, for salary IB is the thing, but you do have to love it as it's a *lot* of work. To be honest, for that kind of salary, the only realistic options are jobs in finance/accountancy, consultancy, law or IT. The latter is something that works if you're already good at it, but it's pretty hard to reskill now to a good enough technical standard. The same with law really. Which leaves the first two.
Accountancy or the more broad 'professional services' are the biggest graduate employers. Deloitte has over 1500 places a year, and PwC very close to that. They all offer internships too, so they're a good place to look to see if it's for you. They pay well - starting salaries are usually ok (£20-30 000) but once qualified they rise quite quickly.
Consultancy is another big employer. The top consultants will pay very well, both starting (£30k+) and rising very well. However they're also *extremely* competitive. People like McKinsey and BCG have fewer than 50 UK places, so they're looking for an awful lot and reject many top applicants. It's worth a shot if it's what you want, but don't hold out too much. Out of the top ones, only BCG to my knowledge do internships, but they're reported to be very good. Your next tier down are still very good graduate employers though, people like Deloitte, CapGemini, OC&C, Accenture, etc. They all have different emphasises, do slightly different consultanct (Accenture are a process and IT consultancy, whereas OC&C are strategy consultants). These are competitive, but being a physics grad from Oxford would put you in a good position. Deloitte and Accenture I know offer internships, and OC&C do their strategy school, but not sure of any others. Salaries start around the same, perhaps slightly lower than the McK and BCG style, and rise quite a lot slower. You're unlikely to ever get on £1m+ salaries here, but £100k+ after 10-15 years is perfectly doable.
Don't overlook IB, there's a lot within it that might appeal. IBD (mergers and acquisitions) is the bit that often appeals for the money at first, however it's *long* hours. We're talking 100+. Expect to be a lacky for the company - all nighters are common, as is being woken up to come into work for something. But the pay is huge, with £50k+ possible in the first year and quickly rising after that.
Trading and sales is the other "front office" position. They're often split, and do pretty much what it says, trading equities, commodities or fixed-income products and selling them to clients. The pay at the top is higher than anywhere (when going to hedge funds, £1bn+ salaries are possible), and even at the lower levels they're huge. They work fewer hours than IBD, but 60+ is still normal and you're personal life has to come second - expect to cancel holidays if work is heavy and that sort of thing. Not many 25 year olds earn over £100k, but most in front office IB do.
Then there's the back office, operations, technology (IT), the heavily mathematical side (quant), structuring products, etc. This is less hours (though still well above 40), and less pay, though start salaries are still easily £30k+ and they do rise well, though not as much as front office.
All departments in IB offer internships, and while they're about the most competitive out there, they're great experience.
In short, if you want that sort of salary, your options are quite limited. If IB doesn't appeal, accountacy and consultancy are the only options I can see, without retraining. IB is a lot of work, to do it, it has to appeal. Accountacy is often seen as a poor-man's IB, however it's a very different atmosphere and is often less pressurised, easier on the hours and, to many people, a bit boring. Consultancy seems the more interesting, with long but not overly long hours (~50 is common) and high pay. However there are few internships, and getting into it can be competitive.
The main thing I'd say is look around for internships, there are many in places you wouldn't expect (I just finished at the FSA and *loved* it). But a dose of reality about salary may be needed - £30k starting salaries are rare, even many prestigious employers are nearer £20-25k at the start. They will rise, but very few people will earn over £100k in the first 10 years of work or so. Those that do are almost all working in finance, law or consulting though. Or are entrepreneurs.