Another PE question

Hi everyone

My son bought a basic fare economy ticket LHR-SYD. When he was at the airport going out, he was charged over 400 to change it to a flexible ticket + airmiles to upgrade to PE.

Coming home he had the same conversation with the airport staff and they offered exactly the same upgrade ticket + miles but for only 200?

Could someone explain why the charge from London is so much more?

Thanks

Some things spring to mind :

1) Taxes out of the UK are higher
2) Ticket basis may have been different, it's not unusual for Virgin to mix ticket classes, ie N one way, and X another (or other variations). This will affect the cost differently depending on your starting Ticket class.
3) Local factors, for example the Las Vegas PE is signposted at around $180 if I remember correctly.

Thanks ukcobra, it's probably a combination of all three. I just thought £200 difference was a bit steep and maybe there had been a mistake in the calculations. He enjoyed the PE experience so it was worth it anyway.