Hi,
You'll find a flight school in North London - Essex but I would also include South and West London in your search for a flight school.
PPL is the foundation of your aviation career, don't let a shorter distance be the deciding factor.
Not saying in the area you specified you won't find a good one, there is a good one, but each student is different so explore the options a bit.
Visit a few schools, talk to students and instructors. It might help to make an appointment as some schools are busy.
Decide which helicopter you want to do the training on, look at instructor and aircraft availability and the overall feeling you have.
Be aware of instructors who are a bit too eager to push you into a trial lesson, most likely they do the job just to get more hours which won't benefit your progress.
Also see if they take time to talk to you without pushing for a trial lesson, if that's the case...run :-) they only see money/hours.
To give you a few names: Flying Pig (Elstree) , Helicopter Services (white waltham) , EBG Helicopters (Redhill), Heli Air (high wycombe).
Asking opinions about these schools is the same as asking who supports Brexit and why :-), you won't get any wiser. Best is to visit and decide.
Good luck !!