What is the best (i.e. cheapest/fastest/simplest) way to reclaim the excess tax i paid in the last tax year?

I started my first job out of university in january and given that i TRIED to claim jobseekers allowance during the period i was looking for a job, i ticked the second box on the P46 when i started work that indicated that i had claimed benefits in the past year. As a result i was put onto tax code 522L and for the last 3 months i've been taxed at full rate (thankfully not emergency).
However I have not earned my 拢5220 for the year(March 31st statement indicates 拢5099 gross TD), and expected to get my tax refunded in my March wage. This has not occurred, and as a result i am over 拢750 out of pocket.

When should i expect my P60 for the 2007-2008 tax year?

What is the best way to reclaim the tax back?
Is there a website that i can visit with some automated process, or is ringing/mailing them the best solution?

You would only get a refund in 2007/08 if your code number was corrected in that year.
Your employer should give you a P60 with your next pay.(Compulsorily before 05/07/08)
Contact your PAYE tax office (reference on the payslip/P60) and they should deal with it fairly soon. Bear in mind that several million others might be doing the same thing.

go to inland revenues website.

they are also by far more helpful than historically now.they have a list of numbers you can call on the website too.