Prague is a lot cheaper than London.
Skype pays employees with title Software Development Engineer II:
US$46k in Prague [0], and
US$82k in London [1].
And I suspect life is a lot more comfortable in Prague on $46k than London on $82k[0] https://www.glassdoor.com/Salary/Skype-Prague-Salaries-EI_IE... [1] https://www.glassdoor.com/Salary/Skype-London-Salaries-EI_IE...