The temptation, especially when doing a very independant subject like History, is to NOT do that much work. It's recommended by tutors (at Cam) that you do no more that 40 hours of work a week; I know people who do more than that, just as I am on eof the many who do less.
Like I say, History is one of the subjects that very much depends on individual motivation. Which is harder, getting up in the morning to go to lectures because you do it every day, or getting up in the morning when you only have an ill-defined reading list and a vague knowledge that in four days time you have to have produced an essay?
The problem is that these arts subjects exapnd and contract to fit the time available. It's possible to get by in History doing 12 hours a week. I know, I have, but generally only becasue I was doing another large commitment such as lighting a show and thus spending something like 50+ hours that week in a theatre!
Anyway, the workload varies, but as Casey and other posters have said it is higher than at other institutions. I met a friend of mine who's doing History at Warwick over christmas, and in my first term I'd read twice as much as him and written twice as many essays. he genrally has four essays to write over a ten-week period, albeit with lectures and seminars and so on as well. I have an essay a week, each of which requiring about ten to twelve books and articles, along with an additional paper every fornight with seminars that needs 5 books or so, and other papers that I'm supposed to be reading for continually. And lectures for three different papers in the mornings.
Ask any Oxbirdge student what they hate most, and they'll tell you it's the workload. Whilst I'm not denying that students elsewhere do work, it's not necessarily at the same pace and tempo.