Just because the can is from England doesn't mean they didn't use crap malt to make the extract.
If it says they used Maris Otter, then it isn't crap malt. It tastes different, and has a flavor profile commonly associated with English beers.
I don't know how you can tell otherwise when it just says "malt extract" -- I guess you have to use it and see how it tastes. Try the web sites or contact info from the manufacturer and see if they'll tell you what they use in it, but who is to say how it varies from batch to batch or year to year.
Most malt extract reminds me of the movie Repo Man with all the generic ingredients. I'd just as much want to eat a can labeled "Food" as I would want to brew with something labeled "Malt extract". Unless your goal is to just make something you plan on calling nothing more specific than "Beer".