OK, I'm going to get laughed at for even trying to attempt to separate a female Pallid from Montagu's Harrier, but lets put the skills to the test!
Wow Niall, I will applaud you for at least one thing, and that is the fact that you acknowledge how difficult it is to seperate female Pallid and Monty's Harriers.
May I direct your attention to this page
that deals in great detail with the matter of seperating the two?
I'm very hesitant to make an ID call on your bird but the more I look at it the more I lean towards juvenile Pallid.
1. The bird seems to show no streaking on the underparts (body). I have to say, the pictures really lack detail so this is not a strong feature.
2. The dark vertical line behind the eye seems to show up well in pic2 which I think is a particularly good feature of juv Pallid.
3. Primaries are clearly barred. Juvenile Monty's would have had almost no barring on primaries. Unfortunately female and sub-adult Monty's would also have had barring on the primaries so it's not clear cut.
4. Pale nape. I'm not sure if this is a reliable ID feature but to my knowledge it points to fem/juv Pallid.
4. I think the strongest feature in all of your pics is the underside of the outer tail feathers on pic3. Juvenile Pallid shows a washed out outer tail feather of which the bands are almost not visible (in contrast to the inner tail feathers). It's almost as if the bands on the undertail stop just before the outer tail feathers.
Whoa! What a ride! I started off being very doubtfull that this bird coud be identified but the more I studied it the more I felt that an ID could be possible and towards the end I "almost" felt confident with juv Pallid. I think this is a very good example of where a bird that would have been unidentifiable in the field became identifiable even with poor pictures.