Does it decrease your borrowing capacity?
As danwatto said, even if you're not using it or paying interest on it, you'll need to include the full debt and the associated repayment in application.
Second Shahin - set it up as a new split loan.
It will look like:
Current PPOR Loan: Not tax deductible.
New equity release loan: Tax deductible (purpose is to invest in property).
Pretty easy to do assuming you meet lending criteria.
Cheers,
Redom