In the UK, Garmin products are not able to use SBAS in place of barometric VNAV, unlike they can in the US - as such it is expected that you don't get LNAV/VNAV. The exact reasons for this are unclear, it appears at least historically the CAA were unsure about its use, and while there are rumours they may have decided they don't mind any more, the databases as produced are still preventing it.
If the approach has LPV minima, then you should get that, and if it doesn't have VNAV, you are likely to get LNAV+V (unless there is something specific about the approach to prohibit it). Annoyingly if there is LNAV/VNAV minima you will never get +V as far as I'm aware, so unless there is LPV you're stuck with plain LNAV
