Once your bridging loan expires, your lender can reinstate your regular repayments. This means that you will be juggling the repayments on two home loans, which can really break the bank. Some lenders will even charge you a higher interest rate as a penalty.
Other lenders take a more hands-on approach and will take over the sale of your old property. Because they are looking to recoup their money quickly, they may choose to sell the house for less than its market value. This means you have less money to pay off your peak debt, and you are left with a higher end debt that still needs to be paid.