Perm interview vs Contract interview

Hello

So assume I get a contract offer accepted (not intereviewed yet)...its only six months (inside IR35 rate is poor) and good chance it probably won't get extended

Simulataneously (applied out of desperation when my contract ended last month) I get an interview with another company (perm salary is also extremely poor) but atleast permanent....and don't have to do with the contract ending malarky again.

I don't know how to proceed with this.

1. Should I proceed with the interview with the permanent company?

2. Or should I say I have an offer accepted else and withdraw from the perm interview and say that I want to stay i contracting? Worry here is they might think that why did choose to apply if I wanted to stay in contracting?

3. Or still attend the (second stage) interview and decline them later - I really do not want to burn bridges as they are the suppler of the product

p.s. I am out of work having contracted for 3.5 years with no gaps