This is not gonna be an answer that spoonfeeds you, but please do bear with me - "teach a man to fish" and all that..
You can check out the acceptance rates for each uni/course here:
http://university.which.co.uk/ Each course has a page that lists various details, including the % of applicants receiving offers.
This site
https://unistats.direct.gov.uk/ is useful for seeing the average UCAS tariff points of each course you are interested in. It has multiple sections per uni course. For example, I searched for UCL History:
https://unistats.direct.gov.uk/Subjects/Overview/10007784FT-UBAHISSING05/ReturnTo/Search If you navigate to the "Entry Information" tab, you can find qualifications and the average points of offer holders.
I think that it's important to point out that a high acceptance ratio doesn't necessarily reflect the quality of the competition. A 25% acceptance rate for History at Oxbridge doesn't sound awfully high, but you can bet that the applicants self-select and that the competition is tougher than other unis with a similar rate.