From a practical perspective it would make no sense
for the British
authorities to pursue these possible infringers outside of the UK.
The primary demand for such material would be in Britain to start
with. The relatively small foreign market for this stuff would
make any reasonably possible victory in such action pyrrhic. The
legal costs would be far greater than what might be won in court.
That's true but the original authors would be perfectly eligible to
sue outside of UK, even if his work is Crown Copyrighted in UK.