Malcolm says the proposed Russian cyber attack is a DDOS or distributed denial of service attack, which is wrong. A DDOS involves enslaving many other computers and servers and using them to coordinate an attack on a single server by overloading it with requests, which is different from patching into an undersea cable and launching an attack from there. In fact it's unlikely that such an attack from a submarine would be successful because of the shortage of dedicated computing power available on the submarine.
The submarine is stated to be in the North Celtic Sea Basin (which is between Ireland and Wales), but the latitude and longitude (48N, 25W) is nearly 900 miles (1400 km) from the tip of Cornwall, in the middle of the Atlantic Ocean. Definitely not in British waters.