Sorry did you (OP) ask for a free upgrade or say you were willing to pay? The last few times we've been away at check-in we were told point blank that there are no free upgrades any more? (Both BA and Virgin)
On a different story when we went to Vegas 13 year ago I was sat in one of the hotels watching Lennox Lewis fitting on the big screen in the sports bar. So as the fight goes on I start shouting at the TV for Lewis to knock the other guy out. At the same time another group of English guys were doing the same thing (seemed we were the only English people watching this fight), so we got talking and it turned out they were Virgin cabin crew, so we talk some more and get onto what flight they will be on coming home. Turns out they were on our flight. Bonus I thought so said "so we'll be ok for an upgrade then" to which they said sure we'll keep a look out for you when you board. Thought no more of it, next day got on the plane sat in out economy seats and got ready to take off. Just after they shut the door one of the guys we meet the night before came over and said "get your things and follow me" which we duly did (everyone around us thought we were being chucked off
), so of we went to some lovely large comfy chairs with loads of leg room better TV screens, better food, and so on. We hit the jackpot
When we got off I had around $80 left over so gave it the crew guy to have bet with next time he went back.
In over 20 years flying all over the world with the big airlines that was the one and only time we got upgraded