The MHRA is the competent authority for a notification scheme for e-cigarettes and refill containers in Great Britain and Northern Ireland and is responsible for implementing the majority of provisions under Part 6 of the Tobacco and related Products Regulations (TRPR) and the Tobacco Products and Nicotine Inhaling Products (Amendment) (EU Exit) Regulations 2020.
The full MHRA contact list is available here if you have any queries.