Tom - ok, although there's a title number for the land outlined in red.
But the post code enables me to identify the farm and the land you are referring to is unregistered, hence you can't see any info for it online
If the extra land should have been included then the route to follow is a request to amend the title.
Contact form and the option "I want to report an error"
However if it's not an error (so the original deeds never included the land) and you are trying to claim the land as it's been used and occupied for a long time then PG 5 explains what's needed
Adverse possession of (1) unregistered land and (2) registered land where a right to be registered was acquired before 13 October 2003 (PG5) - GOV.UK (www.gov.uk)