Thanks for your response
There is recourse (if your friend wishes to) to sue this individual, as clearly they have made the situation worse for him.
However that aside the position would be as this
Earnings £31,000 less personal allowances for 2010/2011 £6475 - leaves £24,525 liable to 20% tax = £4905 plus Class 4 National Insurance which will be £5715 national Insurance free - leaving £25,285 liable to 8% = £2022.80 - so a total of £6927.80 due plus interest and penalties.
You do not advise whether your friend had any expenses arising which he was out of pocket by, but if these were wholly business related, then these can be deducted from the income earned.
Plus even the return filed with £10,000 income would have seen a tax and Class 4 national; insurance charge arise, so this I assume has been paid, and can be deducted from the overall position.
I would advise that your friend should hire a reputable accountant on his return to the UK to
1) amend the tax return for him
2) Negotiate the penalties charged on the basis of what has taken place and the fact that he did not sign the return in question
3) Offer advise on recourse for your friend against this individual
Do feel free to ask any follow up questions, but it would be appreciated if you could rate the level of service I have provided.
4) Ensure all correct expenses are claimed to reduce this tax bill