You might be interested in the Digital Economy bill which will be debated in the House of Commons again on Tuesday 13 September 2016.

http://services.parliament.uk/bills/...aleconomy.html

If eventually passed in this form (see page 17) there will be a fine of up to £250,000 ($385,000) or 5% of annual turnover for anyone who makes "pornographic material" accessible to under 18s in the UK whether commercially or free. So age verification will be mandatory on everything. Affiliates and advertisers will be classed as an “ancillary service provider” if they link to or advertise on any non-compliant site.

It seems to included video, still images and bizarrely even audio. It all hinges on whether the material would qualify for an R18 certificate if released as part of a DVD and whether it was produced "solely or principally for the purposes of sexual arousal."