Skipname,
Banner Towing: There must about two or three companies in the entire UK that do banner towing . From my experience not something for a real low timer to be doing.
Air Taxi: Very few piston twin operators left out there, most will want at least 100 hours multi P1, of which the only way to obtain that is buying hours in the states (kind of pay to fly really) (ok you might be lucky and get to fly dead legs as a safety pilot maybe).
The schools around London are full of instructors who have been stuck full time instructing for 2 to 3 years and not moved on to anything. Look back ten years ago and a lot of the airlines that once took an instructor with a 1000 hours now only take cadets from CTC.
The fact is once you hit a 1000 hours either move onto CPL or multi instructing (btw upgrading to MEI costs close to 10K). If not there is no point persisting with full time instructing at ppl level, all you are doing is keeping yourself on a low wage, it is far better to drop down to part time instructing, go back to your old job and use the additional money to fund something that will advance your flying career (ie: Multi time, type rating or even just some decent ifr touring around Europe in a complex single).
Skipname, working five years as an instructor he has probably realised most operators don't give a flying **** about masses of single engine time.
If he does do a 500 hour scheme he will come out of it with a full ATPL and actually be eligible for some of the reasonably well paid contract work on the A320 in Asia.
I don't agree with pay to fly, I wouldn't do it myself but fully understand why someone would consider it. That said I would never recommend anyone to go full time instructing these days.