In reply to qaboos: MLTA or AMI?
For my money I would invest in an AMI instructor, the MLTA deals with Mountain Leaders and Single Pitch Award holders. If you really want to learn to climb outside rather than just get taken top roping then I would opt for someone with a Mountain Instructor Award (MIA).
I am based in Snowdonia, if you can make it across this way, if not search the AMI database.
Think about what you want the instructor to teach you, do you want to become independent climbers, eventually learn to lead outside, become competent at following more experienced climbers or just have a day outside climbing under someone's supervision?