They will fund you for the length of your current course, plus one year, minus any years previously spent in higher education. This works backwards from your final year.
So if you want to do a 3 year course but have already had 2 year's funding for an HND they will only fund you for the 3rd and 2nd year of your course.
If you want to do a 3 year course but have already had a year's funding at another uni which you left in the first year, then they will fund you for years' 3, 2 and 1, but thats it. if you repeat a year you fund it yourself.
etc.