Hi @James_Kinneir - Sorry to hear Ivan is missing.
I’ve posted the details on the @se23cats Twitter feed https://twitter.com/se23cats as well.
Hope you have some positive news soon.
fingers crossed for you and Ivan.
Ours went missing for 4 or 5 days and then returned, seemingly unhurt if a little hyper.
Do leave anything that smells of him/her outside, and pop out in the quiet evenings to call for them. And do use free missing pet sights.