In this summary of a paper for UCL European Institute, Michael Grubb and Stephen Tindale find that Brexit will reduce UK energy sovereignty 

Leaving the EU would greatly reduce our influence on European energy and climate change policy. The UK has been an active and effective contributor to EU energy policy and spearheaded the EU’s Internal Energy Market (IEM). It chairs the EU’s Agency for the Cooperation of Energy Regulators, and led the EU negotiating team at the Paris climate change conference.