UPVC windows advice needed

[Nicpic]

Hi,
Long story cut short, we had a fire were out for 14 months and moved back home wearing rose tinted specs. My husband and I have found issues which will hopefully be rectified soon but I'm concerned about one issue and could do with some advice as I don't want to be fobbed off.
I noticed that the Windows were draughty, so much so that the curtains move in my bedroom. When I looked through the gap under the window sill I could see that the gap between the external wall and the frame is about an inch with no filler and a strip of plastic stuck to the outside wall so you can't see a gap from the outside. The builder has said that they can't be filled from the outside as the conservatory is in the way so they will fill from the inside and it will be fine.
I am concerned that this could allow damp into the cavity and cause more problems later.
Should the windows be filled externally or is the builder right and internal filling will be sufficient due to the piece of plastic under the external sill?
(Sorry for asking such a boring question but the last 18 months has been a tad stressful and I would like to stop worrying about it now)
Thanks in advance,
Nic

 

[HERTS P&D]

See two links below:

http://www.screwfix.com/p/soudal-window-door-installation-foam-kit-gun-grade/1740h

Andy

 

[ched999uk]

Give your local council building control department a call. Ask for their advice. If you get a helpful person they might even offer to pop round and take a look. As far as I am aware windows installations have to be certified and registered with the Council. Most installers self certify but the council do provide a certification system (at a cost) so they do have the expertise to give a proper opinion.
The other point is that part of the reason for the cavity is to provide an insulating gap. So if the wind can blow straight in from the outside to the inner skin of brick it is negating any insulation that was supposed to keep your home warm.

Forgot to say, I am not a builder but have had some experience with Double glazing fitters and Council certification.

Good Luck and let us know what happens.