As stipulated in the Tobacco Products Directive, e-liquids with nicotine can only be sold in 10ml bottles in the UK. However, there’s no restriction with e-liquids that don’t have nicotine. An example of these would be shortfills, which are nicotine-free flavour concentrates that are available for as much as 50 to 100ml per bottle. You can then add a nicotine shot to these.
In the UK, e-liquids are also only allowed to have a maximum nicotine strength of 20 mg/ml. The manufacturer should ensure these come with nicotine warning labels.