This happens in NA also not just UK
Your internet connection is routed through the UK to reach Japan. This is more common on the east coast, but also possible for west coast residents. You can run a trace route when it cuts out to see the path your connection takes to SE's servers; it cuts out or has an extreme delay at the node geigei posted.
It is likely that North Korea is involved with the activity in the UK. However, since the problem location is neither in your ISP nor SE's control, it's not one that you can readily complain about. I know everyone is looking for a target to blame, but realistically it is not their fault.
As others have posted, using a VPN closer to japan can change your route such that it doesn't pass through the UK. Even if it still passes through that node, you'll be less likely to d/c (the connection between FFXI servers and your VPN won't be severed, and most VPNs are much more fault tolerant than FFXI is so they can recover when the connection between you and your VPN is severed).
To further elaborate, here is a map of the current undersea cabling:
You may not take the shortest route at all times, cables have different owners, partnerships, limitations. If a cable isn't performing well or is particularly bogged down, you might even take a drastically longer route than expected. However, you can see how many of the trans-atlantic cables pass through the UK. A critical point there being attacked will cause speed and connectivity problems for an immense amount of traffic.