I must sound like a broken record to many of you that have heard this before but as far as I know here goes:
No automatics (if you are casught with an auto, you will go to jail) they have been ilegal since the 19somthing offensive weapons act.
You are not allowed to carry any kinfe without a good reason (self defence not being a good reason- dont even mention it) ie. a carpet layer having a knife etc.
the exception being a "small folding pocket knife with a cutting edge of less than 76mm" thats just under 3" to you over the water
However some police forces & courts seem to think that this means that the blade can't lock.
On a daily basis to work and generally around civilisation I always carry a sub 3" locking folder and will argue the toss if I have to.
If you friend is going out in the wilds (such as there is over here) then he should have good reason to have a bigger folder or a fixed blade.
I don't know if the rules in Scotland are any different but if he wants to wear national dress ie a kilt he can then carry a large dagger in his sock, I cant remember what they are called but national dress is an exception to all the rules.
Serrations are not an issue as regards the law however as I am sure you are aware they tend to scare sheeple.
The most important one for your friend is airports. Do not try and take anything with a locking blade into the secure side of the gate (I lost a CF plain edge dragonfly at Gatwick last summer)
If your friend wants any more info of help drop me amil on my workd address
h.wareham@me-electronics.com