Only as much as he would be if he was earning the same amount extra in his first job.
As has been said, the tax will most likely be the same. Provided you earn over £5435 per year in your first job, and overall are still within the Basic Rate Band, then your second job tax will all be at 20%.You will be taxed heavily my friend, so not recommended unless you REALLY need the cash
You only pay NI on the percentage above - you don't lose money for making more. 11% is hardly all of your money. If you earnt £200 per week, you'd only pay £10.45 in NI. The £40 in tax is a bit more though!guess i'll have to work out exactly how many hours i can do extra a week then lol