If you're still here "technically" on simply your passport as a Visitor, I'm not sure I'd take the chance and go to the interview. I mean, it clearly states that you cannot SEEK employment whilst here as a visitor, and I think most employers just assume you are free and able to work when you do the interview, so they might not appreciate it to find out otherwise.
I hate to be a party-pooper on this, but the last thing you need is anything the Home Office can run with to prove that you've broken the terms of you being here on the sort of "permission" you ARE on - that being simply as a visitor.
Really - I would follow each and every rule right now so you can go into any fight with clean hands. It's frustrating to see the *perfect* job slip by - I know because I looked at them all in the papers for the 6 months before the wedding. But really, even just volunteering is wrong on your visitor status - no undertaking of employment, paid or not, is allowed.
Again, I hate to be a wet blanket. But you have to think about the future in this situation, not just right now. And another job will come along when you're all legal and able to actually take it. Honestly, the chances of this place you're talking about being willing to go through all the rigamarole of obtaining a Work Permit for you are slim and none, unless it's an incredibly specialised/hard-to-fill job.
Sorry if that's not what you wanted to hear, hon. You know I'm on YOUR side, though :-/