Hollandaise sauce is not a million miles away from Salad Cream.
No, not a million miles... but there are enough differences that you can't really get them confused. Hollandaise should be rich and unctuous and buttery, salad cream (the bottled stuff, at least) is relatively thin and sharp.
I wasn't sure of the ingredients of salad cream so I just looked it up. Interesting. Apparently, it's not a Heinz invention as I assumed, it dates back at least as far as Mrs Beeton. She makes it with hard-boiled egg yolks, oil, lemon juice, mustard, sugar and cream. The key difference with hollandaise is that it uses butter rather than veg oil, raw yolks rather than cooked, and leaves out the sugar and cream.