i would have thought you can work full time until your course starts, then in term time no more than 20 hoursa week, and full time in uni vacations and also fulltime after your course has finished if your waiting for exam results until your student visa runs out and for not more than 4 months.. but as always check with the immigration people
have a look here
http://www.ukcosa.org.uk/pages/guidenote.htm#workduring
but becareful as
Working more than 20 hours per week in term time is a breach of your visa conditions and you are breaking the law, liable to arrest and deportation. You may also find that you will not be allowed to return to the UK.
Recently, several International students have been arrested and are awaiting deportation as they were working in excess of 20 hours per week.
