I can see absolutely no reason to be an instructor in the UK unless:
a) You have another job and you just do it for pleasure
b) You get to teach something interesting (Aerobatics, instruments)
c) You have your own flight school
Many instructors do it for the hours. If that is the case, I'd do it abroad. I've seen many people move out to the USA (or elsewhere) for 2 years, get their CFII/MEIIs etc..and then instruct for 18 months, often on new aeroplanes. They get visa's sponsored by the FTO, get a place to live and make $25-$30 per hour which goes in their pocket. Ok, not much but after 2 years they walk away with an FAA ATP, 1500+ hours, and a JAR conversion, and the whole lot has actually "only" cost them £30,000 as opposed to the £60,000+ for 250 hrs in the UK.
My mate did this, and came back in Jan. He converted to JAR, did a type rating (paid for by the company) and is now a captain of a turbo prop (interesting flying, not airline) earning a good wage.
Wish I had done it