...so the only option is to put it on an existing UK licence or obtain a new UK licence
Which was the crucial point you omitted to include in your previous post.
The proposed charge for issuing such a
National UK Pilot's Licence in order to retain National UK ratings
is £35 (see p4 of the CAA Scheme of Charges).
However, if the proposed amendment to
FCL.600 IR - General is accepted, this supplementary lifetime United Kingdom licence would no longer be necessary.