Raised case to Cisco in the end.
Cables are Cat6 and connected to GS110
Cable run is nowhere near electrical supplies and had checked all of that previously.
Removed AP, to test locally on the GS110 and still got only 100Mbps. Attempted "Force" link speed to 1Gbps, AP would simply not connect at Gig.
Cisco suggested local session to AP, but that was auto and simply put refused to connect at anything other than 100Mbps.
Awaiting arrival of a new outdoor AP and will replace.
thanks for your help.