Can you actually make a living from being a flight instructor ?
No. Unfortunately the market is in a state where there are plenty of instructors willing to work for very little money, so flying schools have all the power.
Almost every PPL school in the country (certainly all the ones I have dealt with) keep their instructors on a self employed basis, effectively as contractors, so they only get paid when they fly. A typical hourly rate is about £20 per flying hour, and overall in the UK you'd be luck to average 40-50 hours a month, maybe 60 as a high average.
So you'll be earning around £1000-£1200 a month, if you're lucky, but that could be £300 one month and £2000 another, there's no consistency, and certainly no salary.