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The London mayor warned that authorities across the country faced a shortfall of business rate and council tax income.
Khan is taking an immediate reduction to his £152,734 salary, cutting it by almost £15,300, and has frozen pay for his senior appointments at City Hall.
He said: “Londoners did the right thing to tackle Covid-19 by following the rules, staying at home and helping to save lives.
“But now the government is punishing them with a new era of austerity.
“Unless ministers act, the current number of police officers will need to be reduced and it will be impossible to tackle youth violence or make the changes to the London Fire Brigade that are desperately needed after the awful Grenfell Tower tragedy.”
According to the Office for National Statistics, the median wage in the UK in 2019 was £24,897.
This means that in the UK, 50% of the working population earn less than this amount – called the 50th percentile – and 50% earn more than it.
Even with the self-imposed wage-cut, Khan’s salary remains above the 99th percentile.
By contrast, two months ago, MPs received a pay rise of 3.1%, bringing their annual basic salary to £81,932 from April this year.
The increase from the current wage of £79,468 kicked in from April 1, 2020. The body that sets MPs pay has also proposed an increase in budgets for MPs’ staff, support for their welfare, and for security.
MPs’ pay is linked to average rises in the public sector, as determined by the Office for National Statistics.
Johnson’s salary as Prime Minister is £149,440.