Which sealant should I use with UPVC?

[Rupster]

I have a UPVC window in my house which has no sealant between the window frame and the internal wall.

Should it have sealant all the way round, and if so, what would be the correct type of sealant to use? I was thinking of using caulk, but the instructions on it said it wasn't suitable for UPVC.

Thanks.

Silicone I think, but is there plaster missing?

No, there's no plaster missing. I wonder whether it just got forgotten.