There is nothing fraudulent about using a personal loan in the way that you have described, I am not sure why you have been told that?
The advice which you were given would perhaps apply to using a personal loan as a down payment, if using it to gain extra leverage against the knowledge of the mortgage lender, but that is not what you propose at all?
I think the fraud comment only applies if you take the loan for say a car and then later default on it if they then found out you had used it for something else.
Barclays state a personal loan can not be used for: Business reasons, Investments, including buying stocks and shares, Timeshares, Purchasing property (home improvements are fine), Gambling-related expenses, Repaying CCJs (County Court Judgments), A purchase made by combining this loan with any others
The Santander one below mentions property (uk and abroad) unless I am reading it wrong
A Personal Loan from Santander can be used for a wide range of purposes, however we are unable to lend for certain purposes including house deposit, bridging negative equity, property (UK and abroad), land (i.e. for parking space, investment or business), household bills, living expenses, CSA payments, personal tax bills, time share, stocks and shares, gambling, borrowing on behalf of a third party (unless given as a genuine ‘gift’), equity transfer, capital raising and any business purpose. There could be other lending options available to you that you may wish to consider, please speak to a member of staff for more information.