I found it rather hit and miss which tees I could play from on courses there. Some gave me no choice but to play from the guest tees, some let me play from wherever I wanted, some I had to show my handicap certificate and some I couldn't play up because I was with my dad and he wouldn't have been playing the same tees.
I have to agree with whoever pointed out that if these courses were in the US we wouldn't be having this debate because places like ANGC, PV, CPC, NGLA etc. don't allow random guys like me to play from any tees! So its hard to whine all that much if TOC tells you to play from the guest tees.
Obviously the more "touristy" courses like Kingsbarns and Turnberry don't really care what tees you play from, they are only concerned that your group keeps up so they can keep the dollars (quickly converted to pounds before they lose more value) rolling in. But even Turnberry had a few of the Open tees unmowed as a way to prevent play from them. I liked how Muirfield did things, when I played there all the par 4s were played from the Open tees, and the par 5s were played one set up (the par 3s were a mix) I don't know if its always that way or they vary it so if you arrived on another day you might have played all the par 5s back and some of the par 4s up. I ended up playing a course that was about 200 yards shorter than the Open course but one stroke less par (the 9th was a 465 yard par 4 instead of a 505 yard par 5, and plays more difficult because of the location of the bunkers and the turn of the dogleg)
I would certainly enjoy playing there a bit more if I could play the same course they play in the Open, and while I'm not a plus handicap like some here I'm competent enough and certainly long enough to play from those tees, and I move fast enough that I wouldn't delay play for those behind me. But I recognize that a large majority of Americans visiting would also want to play from those tees, and on average are less competent, shorter and slower than I am, so it would be a disaster to allow anyone who asks to play from those tees. Showing a handicap card is no barrier since there's nothing stopping someone from making up scores to get an "official" handicap card that shows him a scratch when he actually can't break 100, and it would be ugly if the starter at TOC could dispute your status if he didn't like the look of your tee shot -- at least based on the stories I've heard from some pretty good golfers here getting nervous and hitting stinkers off that tee!