Are you currently experiencing fasics with atrophy?
This has been said a thousand times before, ALS is insidious. It sneaks up on you and quietly goes to work without you having any idea that something is happening. Some people do notice fasics first, but they do have other things going on that maybe they attribute to a more common ailment, like weakness. They are having a hard time doing certain things that they could normally do, or their gait has changed, or they have atrophy and do not realize it. I think that the most important thing to understand with ALS twitching is that it is almost always confined to the area of weakness. It isn't usually global and it goes unnoticed. The things that get people to go to the doctor are various forms of weakness and upon clinical examination something is seen that prompts a referral to a Neuro, like abnormal reflexes.
If you have atrophy then you should without a doubt have weakness and you cannot pass a clinical strength test with true clinical weakness. Some reflexes can appear to be normal, but in an ALS workup you're going to see abnormalities during the initial examination, whether the fasics are there or not. Most neuros won't even acknowledge a twitching complaint because they are so common and usually benign. I read something from a neuro who specialized in MND that said EMGs are diagnostic tools that are not used to rule out ALS but to confirm it and fasics are never the reason for running an EMG.
As far as the statistics you're looking for... ALS is universal. It doesn't discriminate against anyone and the numbers are two per 100,000 people. Not sure on the number of people in the UK with the disease.
Hope that helps!
If anyone sees anything in there that isn't right, just let me know and I'll correct it!