OK, before I get burned at the stake (on a fire started with a firesteel ), I do carry firestarting kit and understand what a fire can do to help my situation in a crisis.

BUT - thinking about my most likely survival situations, the likelihood is that I will be injured, or night is falling or similar. At which point instant shelter is more useful and acheivable than a fire. Crawling into a survival bag in a shelter spot is more doable than trying to find enough firewood to get a decent fire fed. And in some regions (grassland, mountains etc) trees are not abundant so I just wont have that option - sit on a mountainside in Wales with a twisted ankle and show me how you would build a worthwhile fire.

I'm not saying don't carry firestarting kit, but I would issue a challenge to those who don't carry shelter (garbage bag, poncho, space blanket etc) as to whether they think in a real crisis they could get a fire and a debris shelter together readily?

There aren't any of those.
Its a false dilemma.
Why would an equipped person (reader of this forum), go without shelter?
Knowing how to make debris shelter, good idea.
Planing to use debris shelter instead of bringing shelter, bad idea.
Preparing to fail just doesn't make sense

Absolutely yes. My experience, both my own bad nights and those of others whom I have helped rescue, is that a fire, along with some sort of improvised or carried shelter, is critical to survival. I have also seen the opposite, where three young lads tried to light a fire, were unable to do so, and subsequently perished.

You must consider this question in relation to the wide variety of environments available. There are certainly situations where a fire would not be necessary. For that matter, there are occasions where a fire would be ill advised (think very dry forests with high fire danger).

In an environment where fuel is not readily available, like above timberline, carry a lightweight stove and fuel. Relative to the benefit, it isn't that heavy.

Carrying a bivy bag and firestarters can add only ounces to your load. Why would you not? What is the benefit of leaving vital gear behind?

I quite agree with bigreddog. When I was an ardent young chap, the mantra was protection, location, water, food - and fire was acknowledged to be important for all of them and especially the first two. But that was a general principle. As for Wales, or any of the remote areas in the UK, lighting a fire is not going to be a priority, simply because of the lack of fuel. That's why the advice to those going into those areas has always been to carry wet weather gear and supplementary warm clothing. I wouldn't argue with a tommy cooker for a hot drink, but I think a whistle is a higher priority.

You have to tailor your plans - and your kit - to the likely survival environment.

Yes indeed. The differences in vegetation, weather, and terrain between Wales and some of the wilder tracts in the western US are considerable

One thing to keep in mind is that, shelter doesn't really create heat. It only acts as insulation for the heat you already produce. If you aren't producing a lot of heat (say, you're slightly hypothermic and under-nourished, which is typical of someone forced to survive outdoors), you are going to have a lot of difficulty producing the heat necessary to get warm (at least in the short term).

Fire, on the other hand, is an outside heat source. It doesn't rely on your own body temperature to warm you up. Besides that, it's a great morale booster, it provides light, it's a good signal method, it often helps to keep away critters, it can make water safe to drink, and..through the magic of cooking....it lets you make certain foods safe to eat and significantly more palatable.

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One a side note: A lot of people consider a knife to be the #1 most important survival tool, but I actually think a fire-starting method is my #1 most important item (followed by a good metal pot/pan/cup). I mean, a reasonably sharp edge is typically pretty easy to find in nature....a broken rock can be used to cut cordage, skin game, carve wood, ect...if need be. I can usually make some sort of shelter without a knife, no problem. However, making fire without already being equipped with fire starting equipment, tends to be a real pain in the behind. When you're cold, wet, and hungry is not the time to be expending energy trying to get a bow-drill or fire-saw working.

I do need firestarter... Or not, I don't know. So I carry one, just in case...

A knife may or may not be the #1 most important survival tool based on your location and circumstances, but I think it is certainly the #1 most versatile survival tool. A good knife can add significantly to your ability to make a fire and a shelter, among other important survival tasks.

While it changes based on where I go and what terrain and circumstances I expect to face, my Most Important Gear List always has knife, fire, flashlight, whistle, and signal mirror on it. Fire making is where I have the most redundancy.

Kudos to bigreddog for raising this - I'm VERY skeptical about the utility of a fire in most situations. The number one problem (not mentioned) is opsec - do you think our special ops troops on a three day mission are building fires? Of course not - flame gives away your position in the dark, and smoke gives away your position during the day. Fires require time to gather fuel (most people DRASTICALLY underestimate the amount of fuel consumed by a small fire in one day) and they are terrible for security. I think the reason why we focus on fires is because we like them.

I guess you are marching to a different drummer. Most of us are considering civilian survival situations, not combat conditions. The disadvantages in combat are huge pluses in normal life and in "normal" survival situations, where a fire fire simultaneously signals your location, warms your body and your food, and raises your morale. What's wrong with that?

I can't think of a single instance in my SAR experience where people who built a fire did not pull through, and there are several where people did not, although there was no good reason why they could not have, and subsequently died.

Fire is life.