I'm trying to plot polygons on an OpenLayers map of Scotland which represent the area covered by UK Ordnance Survey maps. These polygons should cover the whole of Scotland and have no gaps between them. However when the polygons (with yellow edges) appear on the map they appear to be misaligned with slight gaps between some of them. The polygons should overlap in places (some locations appear on two maps) but there should be no gaps.
I've checked the co-ordinates (in both their original OS X & Y co-ordinate form and their converted latitudes and longitudes, done using PHPcoord http://www.jstott.me.uk/phpcoord/) and they seem to be accurate and fine. Which makes me think it might be a projection issue, but I can't figure out what I'm doing wrong or how to change it.
I wasn't able to create a JSFiddle using my actual GeoJson file so the JSFiddle below shows my map code but with the GeoJson file missing.
I've validated the GeoJson file and it seems to be ok.