Online Postgraduate (Statistics / Mathematics)
Open University offers a Masters in Mathematics, available to anyone (even outside UK). See http://www.open.ac.uk/postgraduate/qualifications/f04.

A simple Google search on "masters" "mathematics" and "online" or "distance" gives enough results which you can then cross join with university rankings.

Is there a particular area you would like study? If online only, why restrict yourself to EU? (e.g. there is applied math at UW, Seattle etc).