I'm actually in that 40% taxpayer, 3 child position and the actual loss is more like 3 grand of gross earnings as the "family allowance" was paid net of tax.
And while I'm wound up, the statement about the government borrowing more than it receives in tax is not helped when they made great swaths of taxpayers redundant. Public servants are part of that rare breed that actually pay the right amount of tax. People with businesses and I include (especially) self employed consultants, offset much or their earnings against costs (ie those normal things that most of us take on the chin after tax).
And guess where lots of work went after we laid off some of our best talent - yes the same people set up as consultants or private companies doing the job for more money and paying back less in tax. - Rant off