Hi Emma,
For many years, I never had much in the way of friends either as I was always too busy. Now at age 39, I decided it was time to make more room for people in my life and as a result, I now have several friendships -- friends who are like sisters.
Anyway... don't get too down on yourself if you are currently having trouble finding friends, because not everyone you meet is friendship material anyway.
Some people are friendly but they are not really looking to form friendships.
I guess when you encounter people like that... the best way to know if they may be a potential friend as opposed to just being friendly, is if they are consistently friendly towards you every time you meet.
To be more specific... Do they take an interest in you and your life or are they just being pleasant?
If they seem interested in you and your life... that is someone who might be a potential friend.
Another thing that you want to do is try to join some clubs or whatever where you can meet people with similar interests.
And finally the last piece of advice that I have is that you need to be careful and not come across as too needy or too agressive in terms of wanting a friendship with someone, otherwise you will scare them off really quickly.
If you meet someone who is a potential friend... and during the several times you have met, your communications have been pleasant (i.e. they take an interest in you, your life, AND you find them to be interesting as well )... maybe just say something along the lines of :
"You know, we really ought to get together sometime... I'd love to hear more about your _____________ "
(stories, travels, your kids, your hobbies, etc, etc)
If they say "no" than don't push it any further.
If they say "yes" to the idea... let them take the lead for a while... until your budding friendship with them gets more firmly established.
Good Luck,
Cricket
P.S. You mentioned you have a Scottish accent, do you live in Scotland now? I would love to visit there someday. From the photographs I have seen of it, it appears to be one very beautiful place.