I wish I could find documentation or proof. Purely anecdotal experience though haha, and this was a loooong time ago.
Basically in the UK children would have birthday parties and I remember attending at least two.
I’ll tell what I remember in case it jogs any memories from others, but I was a child so logistics are assumptions haha.
I assume the parents would book a “birthday party experience” with the cinema. In this case the theatre would be odeon (biggest chain in the UK at the time). Again I would assume it would be a bulk discount type of thing.
So the group would be about 10-20 kids and you would arrive at the theatre an hour early or something. They would take you into the projection room and show you how everything works, the giant roll of film and give a tour of the theatre and how all the magic works behind the scenes.
Then they would give you a party goodie bag. Inside were the promo cards and some film cells from the movie. The promos were random and if I remember each bag would contain two promos. There was also a movie program, similar to what you would get at a sports game. Some movie snacks and I feel like there was something else but my memory escapes me.
Then they would take you back and you would watch a screening of the film with everyone.
That’s about as much as I can remember.
Here is the brochure you would get in the goody bag:
Sorry for the deep fried image, but I am not with my collection right now. You can see on the right hand side “presented by odeon” which was the movie theatre chain where I attended the parties.
I don’t have a picture of my film cells but have them in storage.
I’ve found other copies of the brochure that are printed by other theatre companies or just blank:
The movie release date in the UK was April 14th 2000 (so quite late comparatively) and Mew was released January 8th 2000, holo version April 2000. I don’t think the Holo version was a possibility in the goodie bags because I never knew anyone to get one and remember trading for mine at a later date.
This is basically all I can remember but maybe other UK collectors had a similar experience and can chime in.
I still firmly count it as a league promo though haha