Well, you bought it, aint no way to return it now, is there?
You KNOW the current unLock will work with the current software and firmware, and you know it will work in the UK. If there is an upgrade, it will (minimum) prevent unlocking, in which case you can't use your phone. SO you loose in that eventuality. If it prevents unlocking but does not brick, you are ahead. If it bricks, you have a previously unlocked phone that you BETTER NOT upgrade.
You gain NOTHING by waiting- do it now.