I've been looking at airspace charts online. The benefit of doing that is you can click on them, see what the restriction is, what the code is and then use Google for further information.
This drone site is actually very useful as you can use named filters and click on the restriction.
No Fly Drones
The area to the NW of Hawarden is Flint Castle. It's a "restricted" area by way of Private Land, By-Laws and Requested Zones.
Further quick seraches show similar areas around Wales which fall under CADW (Welsh Historical Preservation areas) who, it appears, have requested no flying areas around their Welsh monuments/historical areas.