Interestingly I think this an underestimate. A leading city banker - according to NEF - earns anywhere from £500,000 a year, and upwards. He or she will - on average, destroy £7 of social wealth for every £1 paid (mainly by causing financial instability by indulging in risk trading).
Conversely, a hospital cleaner generates over £10 of social wealth for every £1 they earn - around £128,000 a year (mainly by keeping reducing the risk of infection, and MRSA).
The above figure of 27* is calculated using the lowest wage a typical leading city banker earns. At the higher end up to 540 cleaners would be needed.
source: reddit and neweconomics.org
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*actually 27.3, but it's unlikely that .3 of a cleaner would do anything more than bleed all over the place and generate a lot of mess