Gap between (external) uPVC sill and Frame

[MikeSpike]

Had this extension built and bay window (fitted by the builders) several years ago. There has always been a draft on the inside of this room - and randomly today whilst doing the drive cleaning noticed a large gap between the sill and window frame. Is this normal? Should it be sealed with silicone? Have done some online research can't work out if it is for drainage or should be sealed?

Thanks

 

[foxhole]

It allows weep holes to drain and is not a cause of draughts.

 

[ronniecabers]

Foxhole is indeed right it is to allow for drainage at the base of the frames but from those photos it looks like the frame isnt quite sat right on the cill , as the gap looks too large to me, still probably isnt the cause of any draught though.
Is it actually a draught? If you ligbt a naked flame ( such as match or lighter ) , is it moving the flame? Windows always feel a little colder due to natural convection