If you zoom out you will see that the danger area is an irregular shape mainly out to sea. Scrolling the description gives:
Red zones are regulated high-risk areas and operation of your drone may be hazardous or prohibited.
This piece of airspace is in effect between Surface and 22000ft MSL
Activities within this area dangerous to the flight of aircraft may exist at specified times. Notes attached to this area provide additional information. Danger, Prohibited and Restricted Areas are defined according to ICAO International Standards. Regulations governing the flight of drones vary from country-to-country, therefore these areas are included for your information. It is your responsibility to check the applicability of any local, state and/or national laws and regulations which may permit or otherwise restrict the operation of your drone in this area. Unless regulations in your region explicitly permit the operation of your drone in this area, we recommend you do not operate your drone here.
Intermittent airspace are volumes that are temporarily activated, typically via a NOTAM or pre-defined schedule. (My Italics)
So it seems to be an area used by Grey Funnel Lines, operating out of Plymouth, to exercise their gunnery skills. A Notice to Airmen (NOTAM) will advise when the range, or a sector of it, is in use. The great thing about the Dronescene map is that it is fed with live data - when a NOTAM is announced and when it is in force the area affected is coloured in blue.
So you cam male your plans, check before you go and, if no blue areas where you intend to fly, go and have fun!
Further east you will see a similar pattern and warning either side of Portland - Lulworth Ranges.
And an example of a NOTAM local to me, the local cloudpunchers (Royal Artillery) will be playing shoot the drone down at Baker Barracks, Thorney Island:
UAS OPR EXTENDED VISUAL LINE OF SIGHT
Blue zones are advanced notice of areas that will shortly become either red or yellow, while yellow regions with a blue border are notice of a current drone flight.
This piece of airspace is in effect between Surface and 1010ft MSL
This is a temporary Navigation Warning, it indicates a possible hazard to aerial traffic in the region indicated.
Active in 16 hours, 36 minutes
Active: Monday, February 22, 2021 8:00:00 AM until Friday, February 26, 2021 5:00:00 PM (UTC).
Full NOTAM Text
Q) EGTT/QWULW/IV/BO/W/000/011/5049N00055W002 A) EGTT B) FROM: 21/02/22 08:00 C) TO: 21/02/26 17:00 E) UAS OPR EXTENDED VISUAL LINE OF SIGHT WI 1NM RADIUS OF 504843N 0005516W (THORNEY ISLAND AD). MAX HGT 1000FT AGL. FOR INFO 07522 791020. 2021-02-0353/AS2 LOWER: SFC UPPER: 1010FT AMSL SCHEDULE: 0800-1700