Sponsorship Letter

I would like to write to a UK Actuarial company to ask them to sponsor me or give me a school loan for university education in the UK. I want to study actuarial science. Due to my parents inability to finance my education fully,thats why am asking for sponsorship. please advise me on how to write to them and what details to include and not to include in the letter. If they were to give me a loan, i'd like to repay it by working for them till the loan is fully paid...this is how desperate i am for a school loan/funding. please help me out as i want to start my degree in September 2005.I will appreciate your help as I've never written such a letter before.
Thank you