Thanks for the clarification.
Then this is NOT a gift from his father, but proceeds from the sale and it cannot be declared as something it is not (which I am sure you can appreciate) and he should not mislead the bank to state otherwise, or this could have huge consequences, for both this mortgage, the property he plans to buy, and HMRC.
And this can easily be discovered - as to the true origin of the money, by both the bank/building society and HMRC. He should just be honest as to where the money has come from.
As your friend is resident in the UK, and remitting this money into the UK, there will be a considered UK capital gain tax position to consider on this sale (this is where an asset is sold for a profit)
This is worked out, by the sale price, less the value at original purchase/acquisition. This forms the initial gain. From this can be deducted the costs to buy and sell (such as legal fees and estate agent fees (or the equivalent in the country of sale)
After the allowable costs have been deducted, then the first 310,600 is capital gain free (as this is the annual exemption allowance) and the remaining gain will be liable to 28% capital gains rate.
Your friend should alert HMRC to the sale once it has taken place, and ensure enough of the sale proceeds are held back to cover the tax due.
HMRC will then issue self assessment tax return after 05/04/2014 for completion (if your friend does not already complete self assessment) and any tax dye is then payable no later than 31/01/2015 (assuming the land is sold before 05/04/2014)