'this is life in London' which London is that?
Not the capital of the UK where there are numerous vacancies.
Some only pay the minimum wage. The minimum wage in the UK is a great deal more than in USA and probably 70% of the worlds population would like to earn it, instead of the 5p and 7p an hour they earn in places like india and china etc. etc.
Perhaps if you need to spend more than your full time job pays, you need one or two p/t jobs to top it up. Ive worked full time for nearly 50 years and 40 of those had at least two p/t jobs as well. I did send 6 months unemployed, but during that time had two part-time jobs but was still qualified for job sekers allowance.