Cumberland Sausages are basically like English breakfast sausages. About 5 inches long and 3/4 of an inch wide and you fry them. Cumberland ones have a particular kind of spicing in them. There's a website here which might help: https://www.thespruce.com/all-about-british-sausages-4149604

Traditionally Cumberland sausages come in a spiral ring rather than in sausage shapes, but that isn't always the case any more.

Henderson's relish is kind of like Worcestershire sauce, but better, and suitable for vegetarians so more versatile.