Less taxes in the UK means higher take home from the 55k than you would have in germany. And you have to factor in that the 55 figure is probably from a time where GBP to EUR was still 1.4:1. Consider that 55k GBP might have been ~4.5k EUR/mo take home not too long ago vs ~2.5k EUR/mo take home from 50k EUR in germany. Still shitty, but not as shitty as it seems now.

EDIT: Also, using current exchange rates, the cost of living in one of the larger cities (Berlin, Munich, etc) in germany isnt that much lower compared to London anymore.