I will come off as a real smart alec on this I imagine. I did visit Exmoor, but I don't exactly remember the topography, what I saw on the BBC video looked plenty driveable in a 4WD vehicle. First problem I see is dragging hose. You can't fight a 1500 acre fire dragging hose around. You have to have trucks that pump on the go and ride. It is one thing to have to drag a little hose to put a few spot fires out, it is completely useless to try to drag hose on a mile of fireline. The bit mentioned high wind...you can't fight a headfire of any size straight on in high wind, you have to start at the end and catch the headfire. There will be two sides of the fire if it started at a single source, one side will be more or less a backfire, the other will flare from time to time and almost be headfire, most fires from a single source are V shaped, with the origin being the point of the V and the headfire being the wide end of the V. You start at the origin and follow the sides up to the head fire, then come along behind the headfire if you can catch it, the problem is in truly high winds with dry fuel you can rarely catch the headfire, so you set a backfire along some natural or manmade boundary that makes it easy to put the backfire out, it can be something like a road, in lightwind even a cowpath will do, or you simply follow the headfire up the sides until it comes to a natural boundary. Ordinary firetrucks(house pumpers) are fairly useless because they are not pump on the go units, you need brush trucks that are 4WD you can ride and shoot water from.
The part of the BBC video that made me nearly laugh out loud was the commanding officer telling the newscaster they were going to quit for the night because it was dangerous....the best time to fight fire is night because the humidity comes up and generally the wind goes down. 3 factors figure in heavily on brush and grassfires, fuel load, wind(both speed and direction) and humidity. Fuel load is going to be a constant, there is a given load of fuel at the fire scene but the wind speed and direction and the humidity varies with the time of day. The higher the humidity, the less water it takes to put fire out, so nighttime with its normally higher humidity is the time you can get ahead of a fire if you couldn't during the day. I posted alot of fire pics on my gallery bovey, quite a few are from a 2-3000 acre fire we got out in 5 hours using a well placed backfire. We did that with 8 brush trucks and one tanker, and 22 guys.