I've had both (Cafe Nero and Starbuck's), and I can't remember a noticeable difference between the two.

However, if you're really into them, you could always get a milk frother? (I think they go for about a fiver) I found that if you add some sugar and maybe a touch of cinnamon to the milk, froth and pour on top of a cup of steaming Chai you get a pretty good approximation of a Chai Latte.