The HM Treasury 2016 Budget publication has some more information (see below) but lacks detail.
Tackling VAT evasion by overseas sellers
1.218 The government is taking firm action to protect the UK market from unfair online competition. Some overseas traders from beyond the EU avoid paying UK VAT, undercutting online and high street retailers and abusing the trust of UK consumers who purchase goods via online marketplaces.
1.219 Budget 2016 announces action that will help to protect consumers and level the playing field for businesses. HMRC will be able to require non-compliant overseas traders to appoint a tax representative in the UK, and will be able to inform online marketplaces of the traders who have not complied. If traders continue to evade VAT and no action is taken to prevent the fraud, then online marketplaces can be made liable for the VAT.
1.220 The government will also introduce a due diligence scheme for the fulfilment houses where overseas traders store their goods in the UK. This will make it harder for VAT evading firms to trade. While the government continues to take action domestically, the global nature of the fraud means international action is also required. The UK has already raised this issue with EU and international partners and the EU and OECD’s current work programmes include further work to help combat this fraud.