I would think you're first port of call would be the Pakistani High Commision in London or one of their consulates in Bradford, Birmingham, Glasgow or Manchester
"Work and Student Visa
This type of visa requires two to three months to process. Following documents are required for Work and Student visa:-
Job offer letter / letter from Board of Investment;
University / College / School acceptance letter;
Other supporting documents will be required to obtain this visa."
So the website says