Article 101 seems pretty clear cut:
(iii) flights for the purpose of:
(aa) instruction in flying given to any person for the purpose of becoming qualified for the grant of a pilot’s licence or the inclusion of an aircraft rating, a night rating or a night qualification in a licence; or
(bb) a flying test in respect of the grant of a pilot’s licence or the inclusion of an aircraft rating, a night rating or a night qualification in a licence
An OPC or LPC is none of the above so does not have to be carried out at a licensed airfield (or outside licensing hours at a normally licensed airfield).