Currently, drivers of vans greater than 3.5 tonnes gvw require a category C1 lighter goods vehicle licence. Once amending legislation is brought forward, the category B limit for vans with powertrains that are battery-electric (including plug-in hybrids), fuel cells, and which run on CNG and LNG, and LPG, will be 750kg more, 4.25 tonnes.
“We have decided to proceed with those plans in order to help incentivise the use of cleaner fuel vans, while avoiding the regulatory ‘payload penalty’ associated with heavier powertrains (including battery weights),” said Jesse Norman MP, Parliamentary Under Secretary of State for Roads, Local Transport and Devolution, in the December 2017 ministerial forward to a response to a consultation about goods vehicle operator licencing exemptions. Part of that, by the way, is that from May all electric vans from 3.0-3.5 tonne registered since March 2015 will require an annual test in Great Britain). Also, it has proposed removing the current exemption of all electric vehicles over 3.5t gvw for hire and reward haulage.
The current vehicle excess duty regime, which taxes vehicles over 3.5t as heavy goods vehicles, would not be affected by the change.
In addition, in Great Britain (not Scotland and Northern Ireland), the government proposes to increase the weight limits of alternatively-fuelled vehicles to 4.25 tonnes for own account haulage (which are covered by restricted O-licence), as well as for hire and reward haulage.
UPDATED 23/1/17. Removed erroneous last sentence, "Electric vehicles up to 4.25 tonnes are already exempt from the restricted O-licence there," and added new last sentence in third paragraph. The changes were based on re-reading the relevant documentation, which has also been attached as a reference.