A note on some basic substitutions you can make to accommodate differences in what is available in stores.

SUET
Some stores in the US are now selling “beef tallow”. Beef tallow is rendered out suet. It also tends to be painfully expensive.

Amazon.com is now selling Atora suet, which is cheaper than the tallow, but still somewhat costly. Whether it is worth buying for the sake of flavour is a decision I will leave to you!

I find that frozen and grated butter works fine as a substitute.

PUDDING BASIN
The ideal situation is to just buy a pudding basin. They are not too expensive, but they are uni-taskers. Any glass or metal container which is roughly twice or thrice as tall as it is wide will make a decent substitute.

MIXED SPICE
Pumpkin pie spice is fine as a substitute. You can also make your own mixed spice blend to taste, just use the sweet spices such as cinnamon, cloves, nutmeg, ginger, etc.