Demetra,(posted 7470 days ago)Yes it is possible that you will be found out if you lie about your finances as the lender will wish to do a credit check which will show up your credit history. Mortgage debts are normally registered with the council of mortgage lenders (if your lender was a member) Most mortgage lenders check the register whilst assessing your suitability for a mortgage.
However your situation is far more serious than that. If you lie about your previous mortgage debt and are found out you would be obtaining money (a mortgage) by deception which is a criminal offence.
Further more if you did manage to obtain a mortgage your first lender could eventually place a charge on that property and may even be able to force a sale. It would not be wise in any case to have a mortgage whist you have an outstanding shortfall debt.
You need to resolve your financial problems before you seek to secure another mortgage or other loan. Also bear in mind that if you are credit checked a lot in a short period of time it may well hamper your chances of getting any credit at all, as it flags up an alert for potential fraud.
I hope this helps