Just as a note, you *can* enter the country before your visa start date -- but it's sort of risking it at the border. I had to be in the UK for other reasons a couple of weeks before my tier 4 started, so I flew in, told the border agency it was so I could drop of my luggage (and ice hockey equipment, which they were amused by) and then travel around Europe before my course started.
You would have to leave the UK and re-enter, to activate the visa rather than being in on a tourist visa. So like 3 weeks before my course started, I went off to France and Belgium, and no problem at all to activate the visa from Belgium.
So it's possible. But again, I could have been refused at Heathrow, so it's probably not advisable.