what is "ground mixed spice" as cited in a recipe?

Side note. I have made the Rose Bakery’s “Savoury Carrot Cake” for about ten years - it’s a fabulous non -sweet riff on the usual. Great for snacks with a hot drink or glass of wine. If you’ve not yet tried it, add ut to your “make soon” list.

Using search engines has fallen out of fashion over the past five years however they can still be useful occasionally.

Entering "ground mixed spice" into DuckDuckGo provides a number of results including #2

https://www.bbcgoodfood.com/user/388309/recipe/mixed-spice

and #3

https://www.nigella.com/ask/ground-mixed-spice

which indicates that mixed ground spice is a commonly used baking ingredient in the UK.

The latter result is a particularly reputable TV chef and cookbook author. Nigella Lawson suggests US pumpkin spice as an adequate replacement for UK ground mixed spice.

Both articles propose instructions on how to create your own from individual spices.

Anyhow best of luck.