Yarnfield is a village in Staffordshire, England.
In the GB data, I could find two references to "Yarnfield".
This one is an unrelated civil parish in Wiltshire:
7297660 Maiden Bradley with Yarnfield Maiden Bradley with Yarnfield 51.14386 -2.28521 A ADM3 GB ENG P8 00HY148 0 189 Europe/London 2010-05-25
The Yarnfield in that name comes from a deserted mediaeval village, and Maiden Bradley is mentioned in the data as a village in its own right, so all good there.
This second reference is a place in Yarnfield, Staffordshire:
10105848 Yarnfield Park Training And Conference Centre Yarnfield Park Training And Conference Centre 52.89494 -2.20017 S HTL GB ENG M9 41UG 41UG034 0 109 Europe/London 2015-02-19
You could probably get away with repurposing those coordinates for a new Yarnfield "P" entry but it is quite north off the centre.