Unfortunately the bank can just pursue you however you can then pursue your ex partner in accordance with the the Civil Liability (Contributions) Act 1978 see http://www.opsi.gov.uk/acts/acts1978/PDF/ukpga_19780047_en.pdf . If your ex partner becomes bankrupt or enters into an IVA as he will technically be a man of straw there will be no real point in pursuing him. If you wish to pursue him and believe he has equity go to a solicitor who may be able to help you put a charge against his property.
If he enters into a IVA any secured debt is dealt with separately and remains secured the IVA is only for unsecured debt. Quite often an IVA supervisor places a restriction on the property preventing it from being sold without his consent and therefore he couldn't dispose of the property without the supervisor knowing and the supervisor has a duty to all creditors however your security ranks higher than all the unsecured creditors so you should be ok subject to negative equity.
In a bankruptcy again the banks security will have to be satisfied before any unsecured debtors are paid.
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