Jelly in Canada = Jam in the UK and we don't have grape flavoured jam here... good job I live with a canadian
The grapes we have in the fruit section are not concord grapes unfortunately, but you can buy Welch's grape juice in Tesco, it's isn't usually in the fridges though - it's with the fruit juice cartons. Tesco do their own version of grape juice but it's not concord grapes they use.
Welch's has a very distinct taste and not one we're overly familiar with here but it is very nice especially after a few glasses. I've been through 2litres over the past week or so and now start to crave it!