I always heard it as "Jell-o", not "jelly".
Jam has small bits of fruit (usually like strawberry/raspberry seeds). US jelly does not since it's made from juice or syrup. Preserves are the kind with bigger chunks of fruit.
Redcurrant jelly: https://www.bbc.co.uk/food/recipes/redcurrant_jelly_26005
The whole jam shelf at Tesco, including "Strawberry Seedless Jam" (shouldn't that be "Seedless strawberry jam"? The adjective order sounds wrong otherwise) and "Strawberry jam": https://www.tesco.com/groceries/en-GB/search?query=jam
"Conserve" means "add £1 to the price".
They had a studio down on Vermont or something in LA and had to change the mural on the building to update the name.