Long story short - yes you can get into both as long as you get good A levels. At Cambridge they do a single honours Philosophy course which has a very mathematical/logic-based focus.
Thinking about Oxford is more complex as there are no single honours degrees but many joint honours degrees. These range in focus and often place heavy emphasis on admissions tests which could help make up for GCSEs.
What to do in preparation? Go to the Cambridge masterclass and enter some of the philosophy essay competitions. Read books with an intense focus. When reading, answer each of these questions:
1) what is the author saying? Put it in your own words, precisely and concisely.
2) does this tie into anything else you’ve read/studied/considered/heard etc
3) what do you think about this suggestion? Provide logical support or criticism of this position.
4) how would this effect other positions or ideas if true or false? Think how you would neatly explain this
I genuinely believe that reading the Stanford’s Encyclopedia of Philosophy (SEP) or Internet Encyclopedia of Philosophy (IEP) is generally more valuable than reading original texts since so many of them are complex and hard to understand. Once you understand the topic having used the online SEP/IEP, I would suggest reading original authors on that topic. This will allow you to have a genuine and well researched understanding of the topic. SEP and IEP are much much simpler to understand and perhaps more ordered in their approach.
Depth of reading massively outweighs breadth of reading and this should show on your personal statement. I would suggest writing 1600 characters on one topic, 1600 on a second topic and the remaining 800 on extra curricular activities.
PRACTICE LOGIC. Not formulaic but WRITTEN logic. I cannot express how important this is. In both my philosophy interviews I was asked some really tricky logic. By complete chance I had studied logic to that level before and using that prior knowledge, I was able to get these questions all right. This is a good beginners guide:
http://www.ilovephilosophy.com/viewtopic.php?t=152732Work experience, study places etc are of no use unless you can tie them in to some form of philosophical thought. Note that oxford and Cambridge (but Cambridge in particular) are not really fans of continental philosophy. That means they’re not into Sartre, Derrida, Spinoza, Nietzsche, Hegel, phenomenology etc. The sort of stuff they like are: epistemology, logic, ethics, political philosophy, metaphysics, philosophy of language/maths/science, philosophy of mind.
A personal suggestion is to think about paradoxes or moral dilemmas and consider what you would say if asked to support or condemn EITHER position. Do loads of practice interviews with friends, family, teachers or other experts.
It’s important to note that almost everything you do (reading books, magazines, articles; watching talks, films, documentaries; going to lectures; listening to podcasts; writing essays, essay competitions, EPQs; debating, going to clubs or societies; doing work experience/placements etc) are ONLY useful insofar as to show your interest in the subject IF YOU CAN ACTUALLY USE THIS TO ENHANCE YOUR UNDERSTANDING AND DISCUSSION OF A SUBJECT. I cannot stress this enough. My friends read like 100 books but without understanding them properly and got rejected even though they mention all of this in their statements and interviews. I read in super detail throughout - in fact, the day before my interview I read 30 pages in depth about one subject and guess what? It came up in my interview, and I was able to tackle the subject well and actually engage with the interviewer. Anyone can read philosophy - only good students can understand it fully and only the best students can discuss it with ease and sophistication.
A quick note about your grades: more important than anything, however, is to knuckle down and get good AS and A level results as without them you can’t go. Also, make sure you stress all your contextual factors in your application so that you’re treated fairly. Good luck, and I hope this helps! PM me for more help if you’d like