Tim, I'm pretty sure you can get it done at any optometrists.
Incidentally, I know you've been at all the desmo circuits, with maybe the exception of Castle Combe, but you fancy a track day at each before the racing? I've posted in the TD's section about Cadwell and Castle Combe and am looking at Donny days etc as well.
Tim book in a t Specsavers or possibly boots for a eye test and explain why you require it. Take the ACU Licence application form along with you and get the optician to fill in the relevant bit.
Tim You can download the form from yhe ACU website and the fee for the eyesight test is around £20. Weeksy put a link to the ACU info in one of his posts on the Desmo Due series and going racing
Boots Opticians will do it, and they charge £15. Just let them know that you need your form signed when you book - they shouldn't charge you extra to do this.
If your company requires you to use a monitor, they may also pay for your eye tests - worth checking out although at £15 it's not going to break the bank!