NHS Choose and Book

I had myself a regular sight test. Vision is at normal Steve Austin level, but I need to have myself some extra glaucoma tests. So, the opthalmist tells me she's going to refer me, I don't have to do anything else.

Today, the letter from the NHS arrives. Name, address, and some instructions which basically say:-

1. Go to the NHS Choose and Book website
2. Find a hospital I like the look of
3. Phone a number during office hours.

Why can't I just book it? Print a code on the letter, let me enter it and just pick the date and place? Wouldn't that be more convenient for me and cheaper for the NHS?

How much did this system cost the NHS?