I got this reply from MHRA:
Regarding your query, yes, an IMP manufacturedwithin the EU needs to be QP certified even if it is going to be used inclinical trials in territories outside of the EU only.
This is based on Annex 16: General Principles; Theprocess of batch release comprises of: iii. The transfer to saleable stock,and/or export of the finished batch of product which should take into accountthe certification performed by the QP, and the Process of Certification:1.1. Each batch of finished product must be certified by a QP within theEU before being released for sale or supply in the EU or for export.