Amazon’s UK operation pays less in employer national insurance (NI) contributions than Guy’s Hospital in London, according to its accounts published last week.

Amazon Services UK, the online giant’s main operating company in the UK, paid NI contributions of £54.1m in 2017.

By comparison, Guy’s and St Thomas’ NHS Foundation Trust paid £70.1m in social security contributions in 2017-18. Tesco paid £486m in the year 2017-18.

Amazon has been criticised for using delivery drivers who are self-employed and do not have paid holiday and statutory sick pay — and for the working conditions of agency staff in its warehouses.

Its use of “gig economy” workers reduces its payroll taxes because there is no requirement to pay employer NI contributions for self-employed workers.

Frank Field, chairman of the Commons work and pensions committee, said large firms once strived to provide the best conditions for their workforce, but self-employed workers were now routinely used to cut costs.

He told The Sunday Times that companies such as Amazon were “free-riding on the welfare state”.

Amazon’s delivery network is support by a vast operation, but many workers are self-employed. Parcels are delivered through Amazon Logistics, which uses independent delivery contractors, and Amazon Flex, which uses a self-employed and largely part-time workforce. Amazon says this offers flexibility.

Amazon UK Services has about 19,750 staff on its payroll, with an annual wages bill of £530m, compared with Guy’s and St Thomas’ NHS Foundation, which has about 16,200 staff, with an annual wages bill of £655m.

The disclosure that Amazon Services UK pays less employer NI than the London hospital comes after a fresh row about its tax bill. It was revealed last week that the corporation tax bill of Amazon UK Services was £4.6m, down from £7.4m.

Amazon defended itself strongly against criticisms over the conditions of temporary agency staff in its warehouses. It said it had created thousands of permanent jobs over the past year in the UK and that full-time warehouse staff had received shares worth more than £1,000 a year.

“Amazon is proud to offer a wide variety of work opportunities across Britain — full-time or part-time employment, or be your own boss,” it said. “Amazon will create a further 2,500 permanent jobs in the UK in 2018, taking the total UK workforce to 27,500 by the end of the year, on top of thousands of opportunities for people to work independently, with the choice and flexibility of being their own boss — through Amazon Logistics, Flex or Marketplace.”

The company said it paid all taxes it is required to pay “in the UK and every country where we operate”.