What does it take getting into Oxford? Watch
They say this:
"Applicants interested in applying for Fine Art who are studying for a BTEC National Extended Diploma (BTEC) will have to submit a portfolio of work, and an offer will require candidates to achieve DDD grades. Tutors welcome applications from those who are engaged on a BTEC National Extended Diploma Art and Design course where there is a substantial element of both Fine Art and Art History. Please note that because of the practical nature of the Fine Art degree, which also includes a substantial theoretical component, a candidate who has successfully completed the BTEC may be well suited to the content and structure of the degree course at Oxford."
So yes, you would have every chance.
Hope this helps