Usually in the first term everyone starts at the same time, regardless of the course.
Generally because of accommodation and stuff like that. Other terms may be different, and in second and third years you may go back a lot earlier. For example, I started my course just after freshers week this year (1st year), but I start lectures on the 4th of September in 2nd year.
You won't miss out on freshers week. Its usually when you enrol and get finance confirmed too.