Hi Pk31,
Thanks for your post and welcome to the Forums. It's really great having you on board with us in the Community.
I'm sorry to hear that you've had to swap SIMs. We've recently sent new SIM's out to facilitate the completion of our migration from EE to Vodafone.
In order for the SIM to be successfully activated, it will need to be done in the UK. Once activated, the current SIM will stop working. The 4-5 day delay between activation and using in your phone will be fine.
Please let us know if you have any further issues.
Thanks,