Hi @jamesward

I would recommend taking a look at the following article for instructions on how to convert from CSV to spatial geometry. This article demonstrates how to create Shapefile points from tabular CSV data (with video):

https://knowledge.safe.com/content/kbentry/1493/index.html

The following article covers creating points, lines, or polygons from CSV:

https://knowledge.safe.com/articles/56486/converting-from-csv-data-2.html

To convert your data to British National Grid, you would need to define your source coordinate system and use one of the Reprojector transformers within your workflow to reproject the data. For this part, I would recommend this article:

https://knowledge.safe.com/articles/585/using-coordinate-systems-within-fme.html

Hope this helps,

Debbi

Many thanks @DebbiAtSafe