A recent study from the Mental Health Foundation estimated the prevalence of chronic insomnia in the UK to be around 8-10%, and possibly as high as 15% for those over the age of 65.
Professor Colin Espie's organization collected the survey data. He describes insomnia as a "disorder of arousal" - apparently, insomniacs have higher levels of arousal at all times (both of the mind and body), making it difficult for them to shut down and fall asleep.
So what's the solution to this raised state of arousal that insomniacs have to deal with? The primary recommendation is CBT - apparently, 70% of insomnia sufferers show some level of improvement after a course of talking therapy.
The challenge lies in making this form of treatment accessible to more people.