Facebook CEO Mark Zuckerberg. Drew Angerer/Getty Images

Facebook has calculated its corporate tax bill at £5.1 million for 2016, despite pre-tax profit coming in at £58 million. Revenue quadrupled year on year to £842 million. The company reported a £41 million loss in 2015.

The social network has altered its business in the last year to book its UK ad revenues through its UK operation, rather than through a Dublin operation which pays less tax. The change was expected to generate millions more in tax for Her Majesty's Revenue and Customs. It's still an improvement on last year, when Facebook ended up with an £11.3 million tax rebate.

Notes to Facebook's 2016 accounts show that it has calculated a corporate tax bill of £5.1 million for 2016. But the filings also show the firm expects to recover or offset £2.6 million of that against future tax liabilities.

Two chartered accountants consulted by Business Insider described the company's accounts "an exercise in opacity."

Another note shows that, if Facebook paid 20% corporation tax on profits, its tax bill would total £11.7 million.

Facebook's accounts also show it has 960 employees in the UK, and that it paid out £104 million in wages in 2016. If you include £77 million in stock-based payments, the average wage comes to £188,500.

Facebook UK's parent company reported $26 billion (£20 billion) revenue for the full-year 2016, on profits of $10.2 billion (£7.7 billion).

A Facebook spokesman said: "Last April, we actively chose to reorganise our company structure to record revenues from our large UK sales customers in the UK. We believed this would provide greater transparency on our operations in London and be easier for people to understand. These accounts reflect that change. We continue to invest and expand in the UK, employing 1500 people in our new offices by the end of this year, which is also home to our largest engineering base outside the US."

Facebook's UK accounts come as regulators and governments take an increasing interest in how Silicon Valley's tech giants structure their businesses to pay minimal tax. The EU just slapped Amazon with a €250 million (£221 million) fine by the EU over its tax setup in Europe. The European Commission ruled that the company's tax deal with Luxembourg was illegal. Amazon said it would appeal the ruling.