In my experience it depends on the work. For consulting jobs where you go sit in a bank or whatever and bash out code onsite all day, £300 is low. But for freelance work, remote work, it's much harder to find anyone who will pay £300, let alone higher. It's not impossible but there's much more of a race to the bottom in the latter jobs than there is in the former.
Yep. It depends on the type of work, type of experience and type of clients. You might strike it lucky with a small client, but it's more than likely going to be low. For new media agencies, they will have years of experience with freelancers, so will push the price down to fit their budget. For big business and public sector, they aren't that bothered, plus you normally need very specialist (and expensive) training to do their work.
I disagree, the distinction between a contractor and consultant is not that one is on site and the other offsite. Many freelancers will work at the client's office if need be.