The most obvious difference is the colour of the camo - British ones are green, brown and ochre; Belgian ones are dark green, light green and brown. Also, the Belgian ones are made of a canvas-type material.
Belgian...
British...
You've got nothing to ein, zwei, drei, vier
But the most noticeable difference when worn is the length. Belgian ones are a bit short.
The Belgian ones are water-resistant - they have a plasticised inter-liner (which is usually stiff and crunchy with age). And a natty drawstring waist!
Price difference too - Belgian £30, Rangercamp Denison £100
Slightly off topic - SoF have reduced their full zip Denisons to £100 now, well they had to didn't they!
Used to have a very nice Belgian smock-in details an exact copy(but in the camo shown) of a 2nd pattern WW2 smock with the bonus of it being waterproof and very hard wearing.-To be honest if i could find another for a decent price i would snap it up 
They are a bit short.
The one mentioned above while the camo was different it was spot on feature wise.Ive seen around 3 or 4 different types in the camo shown which are all pretty bad realy-Some similar to ww2 2nd pattern but the half zip goes down 3/4s of the way down-Others with half zips but pockets have 3 brass press stud closure and the worst are full zip with a brass press stud storm flap and the 3 brass prress stud pockets.
I hope this smock doesnt belong to anyone on here as i dont want to offend anyone but in my humble opinion if anybody was thinking of buying a Belgian smock this type is the worst of the types i have seen-
http://cgi.ebay.co.uk/AIRBORNE-SMOCK-DE ... dZViewItem
Now cheaper repros are available it is easier to get a more authentic smock .
BUT... Belgian smocks are still totally cool for our games (although for PBI we'll happily lend you an authentic repro until you can get one)
"I think we are in rats' alley - Where the dead men lost their bones."
I have the Belgian 1, I got it for Arnhem. Could do with a nice British looking 1, but not quite ready to fork out! Especially when I'm lining up for a BD Jacket and Tommy Helmet. If some1 could lend me a British 1 for Varsity hopefully I wouldnt look too out of place hehe
There will be several people in Belgian ones...
Anyway you can borrow my full zip one for the day if you like... (look after it 
)
That would be very kind of you Yithster!