I think you are British, that's the polite form in the UK where I come from. In the USA if you try this it's pretty common for people to say yes they would like it. Different culture!
I'm not an expert on manners, but I don't think there is any polite way to claim yourself an extra pork chop to the exclusion of others.
I should have put a note in there about cultures in my original post as I suspected as much about there being differences. I suspect in non-Western cultures too that this behaviour isn't a thing as well.