I think they run bigger.
If there’s an H&M near you, you could go in there and try on some sizes to see what fits you best since they use UK sizing.
It is the american size +4 so a 2 will be a UK6. ASOS usually runs true to size so it’s not likely that you’ll need a bigger size than 6. Also, I wouldn’t rely on their size chart as they sell so many different brands and most of them don’t meaure according to that particular chart.posted about 5 years ago