As far as my investigations were concerned, HSBC will be less concerned about security if you are likely to pass. However, anything you put up would obviously be a bonus just don't offer it until you think you have to! In fact, I would say never offer any security until you have to.
Just a quick note on Pilot Assist. The 'price' includes PPL, hour building, night rating, etc as well as ATPL, CPL/IR. If you just do the bits you havn't got the price, you will find, is very competative. Just ask em for a brochure or download it from their site.
BTW, I have nothing to do with pilotassist, just thought I would point out what I have noticed.
The reason HSBC supports this type of loan for pilots is, as far as I can work out, the link between them, the Swire Group and Cathay Pacific. Swire Group being, or appearing to be, the holding company for both. Maybe somebody can clarify.