Bluesteel705,
I went to the HSBC in Leeds a few years back to enquire about a £40K PSL loan; at that stage I was making enquiries. They said that the loan must be secured on the house.
If I remember correctly, I think that they said that £10K was the maximum that they would lend unsecured. However, people on this forum have reported borring much more than £10K unsecured. I think the branch you choose to visit is key. Apparantly (from this forum), the Oxford branch seems to be the one to visit.
Incidently, I didn't take the loan in the end.
POL