This page suggests you can still order additional IP addresses
in blocks for a monthly admin fee (single fixed IPv4 as standard).
Note that you'll also receive a delegation of globally routeable IPv6 addresses without additional cost, which can be used on network(s) behind your Fritzbox (supplied by Zen, or if you substitute your own compatible router).
In general regardless of UK provider you would be asked to justify larger IPv4 ranges via a RIPE form including your efforts towards efficient use of address space and transition, though that might only apply for more than a /29.
prlzx on Zen: FTTC (VDSL) at ~40Mbps / 10Mbps
with IP4/6 (no v6? - not true Internet)
Edited by prlzx (Wed 04-Nov-20 09:02:57)