I have recently won a court case to re-possess my house and land on which it is built. Of course being a foreigner I cannot own the land and I have either to sell it to a Thai National or transfer it to one within a set period of time.

My land office have told me that there are three taxes I have to pay: One is a 2% property transfer tax. Another is 3.3% tax because I bought the house less than 5 years ago and the third is a tax that no-one can fully explain of 2.2%. The best the official can do is to say that it is a business tax. I don't have a business so am I missing something here. Anyone who can explain this third tax to me please.

The standard transfer taxes for immovable property in Thailand are:

1. Transfer fee of 2 percent (%) over the appraised value (as opposed to registered sale value) of the immovable property at the Land Department
2. Specific Business Tax is charged over the appraised land office value or actual sale price (whichever is higher). The tax rate is 3,3% and consist out of an actual 3% Business Tax + a local maintenance tax of 10% over the amount of business tax. The property transfer is not subject to business tax if the seller is an individual and has possessed the property for more than five years before the transfer. Companies generally must pay business tax irrespective the period of ownership, however some specific companies are exempt from Specific Business tax.
3. Stamp Duty is charged at a rate of 0,5% over the government appraised value or actual registered sale price (whichever is higher) has to be paid if the sale is not subject to Specific Business Tax. In case Specific Business Tax and Stamp Duty has been paid to the Land Department, the seller has the right to claim for the refund of this amount within 6 months after the payment.
4. Withholding Tax for individuals depend if the immovable property is acquired by inheritance or gift or if the sale and purchase of the property has a trade or profit seeking purpose or not. Withholding Personal Income Tax income shall be calculated at progressive rate with a deduction depending on the number of years of possession or if the seller is a company (but there are specific reductions or exemptions).
5. Withholding Tax for companies is fixed at a rate of 1% over the registered sale value.

We can assume that the 2.2% is the land office's calculation of withholding (income) tax per #4 above.