I like Marmite, but I can live without. You can often find it in Indian grocery stores over here. Paxo stuffing & Bisto are not a patch on real stuffing and real gravy so I always make my own ('cept when Tree does the cooking, which is most of the time, and then she makes her own).
Spam's American.
Salad cream can be made by adding vinegar and mustard (Colman's, or hot Chinese) to Mayonnaise.
We make our own steak pies (Tree doesn't like kidney).
Good strawberry jam 'can' be made. The secret is to pick your own strawberries and make the jam the same day and add juice of a lemon to every two pounds. Otherwise you'll have to add pectin.
I always make my own Custard. Tastes just like Bird's. Unfortunately I don't use a recipe, but here's the way it's done...

Heat the amount of milk you need with sugar, vanilla extract and yellow food coloring. Taste it to see if you've added enough of each. Before it boils add cornstarch (Mix it with cold milk first), the more cornstarch the thicker the custard.

Bert.