Firstly I just want to say DO NOT stop giving him the Becotide WITHOUT medical advice.
I have asthma myself and was having a particularly bad time the same time as Twiglett (remember posting to each other on same thread).
The Becotide (brown inhaler) is the Preventative which works by keeping the airways open and relaxed, therefore if used and working properly should mean that you will not be using the Salbutomol (blue) at all, or at least not frequently.
In my experience, GPs are a waste of time when it comes to asthma. Most of them just throw inhalers at you without checking that you are using them properly and don't bother with follow-up appointments to assess you.
I have a wonderful Asthma nurse who insists I call her at any time if I'm suffering and likes you to attend regular clinics to monitor.
My friends little boy has asthma and she kept stopping his Brown Inhaler, but then he was regularly having attacks, the last 3 he has been hospitalised. Also needed oral steroids regularly. She has been told she MUST keep up with the Brown in order to keep the asthma under control.
The National Asthma Campaign website has been VERY useful to me - my friend also consults this now.
Like Twiglett, I'm currently at 1 X 1 puff of Brown 2 times a day and haven't used my Salbutomol for about a month. My 2 triggers are cigarette smoke and colds (most common apparently) and have been advised to increase my Brown at the start of a cold and to have 2 puffs of my Blue inhaler if I'm about to go anywhere smoky.
I really DO NOT recommend stopping the Brown then relying on the Blue in the event of an attack - and I talk from experience (used to become very slack with the Brown).