If there was any query by revenue, actual facts are used and not words written by a bank official. In any case, the bank only reports if they are supicious of where the money came from, so for ease of paperwork, "gift" is probably right.
The only "gift" is the value of the interest and this would be well under limits.
Your bank statement and your brother's bank statement will show the tansaction. Similarly when the hosue sells, the reverse transaction will be shown.
Nothing whatsoever to worry about especially as the giving and return will take place in the same tax year