@GraemeD O2 doesn't operate a live stock reporting system. Whatever you ordered is most likely out of stock. You will receive a confirmation email, but not until your order ships.
Customer service numbers are here: Guide: Coronavirus Community Help and Support Use the Upgrade, Lost/Stolen, or Fraud option to get through. Otherwise you'll just be disconnected.
Alternative advice from an O2 Guru on how to get through.
Call 202 from your mobile.
When it comes to the reason you are calling, stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
Best time to call is 8 am.
Unless there is a glitch with the system, which I doubt, your order won't be coming today.
Also as @Bambino said, O2 do NOT operate a live stock system and although the phone may be showing as in stock, from our experience on here it probably isn't.
The system is, they receive your order and confirm it via email. Then (usually the night before) you will receive a dispatch email. Once you have received that, you will find you can track it in My O2.
Give O2 a call and check on it's status.
Track usage, upgrade and get support with the My O2 appDownload My O2