Under the TPD rules in the UK tanks with a capacity over 2ml have been prohibited for the last 3 years but I have experienced no problems importing non-TPD compliant tanks and do not know of anyone who has. Theoretically they can be confiscated by customs - but to enforce this customs officials would have to open every single package.

The question you should ask yourself is how thorough are your customs officials and are you willing losing any non-compliant items. You will always be able to import items - the legality and compliance is your responsibility, not the sellers.