The denomination of the excercise price for SAYE-options for normal employees rather than top managers is based on the price obtaining when the option is granted, minus a fixed percentage. The fixed percentage is dictated by the Inland Revenue for SAYE schemes. I seem to remember it is about 20% but someone among you probaby has an accurate figure.
The objective is to ensure employee buy-in to the future of the company, thus ensuring increased productivity and, hopefully, paying dividends in terms of increased profits. These profit increases are expected to pay for the scheme.