So, company has to pay to this agency 80 GBP per hour for you and you like developer will have something about 10-15 GBP per hour...

Then things must have changed drastically since Andy and I were living in the UK. When we lived there we always worked through an agengy because it made things easier - we did not have to worry about accounts receivable and when we worked in Holland, we did not have to worry about the currency conversions from guildars to sterling.

However, our agency (and most of the agencies that we had heard about) never took more than 15% - 20%. This seems pretty fair to me considering the fact that the agencies take the risk of being out the money that they have paid the programmer if the client goes out of business or does not pay the bills for some reason.