Topping/fimming/LST all absolutely positively increase yield. If the idea of cutting your plant makes you feel uneasy look into LST (low stress training) you just tie down branches and can easily get more herb
Any person that is not getting their plant to produce at least 16 to 20 ozs. per plant should not be advising, they should be seeking advice. Go to a good site with sound advice and lots of experience, like Dude Grows.
England...
If you're growing them indoors..with most light setups..its best to top as you get a more even canopy and less shade..outdoors Mr sun will blast lots of photons..so not as important.
I would even suggest you try FIM'ing..pinch of the top..leaving a small clump of tissue and partial leaf structure where the nodes were connected..(google it) this should create 4 colas for you..
Hey, growing is about learning right? And photos are more forgiving than autos with respect to stress training.