O2 UK upgrades won't budge on SIM-only pricing. Can they?

[Jezston]

I've been with O2 for about 10 years and have usually worked myself out a decent deal at the end of each contract.

Last year that didn't end too well as I wanted an HTC One S, but whatever they offered me as a combined phone / contract it was significantly cheaper to buy the phone outright and stick to my (then very good) sim only contract. Which I then did.

This year, I'm still on my 2 year old contract (600 minutes + 300 O2 to O2, 500MB data,