Uneven base with purple dye

Both of those colors you got are very blue based purples, so if you don't have a clean blonde(at least yellow, no orange) you will get a very murky brownish color since blue tones orange.  You could probably get away with a very pink based purple as they are much more forgiving to a less than perfect base.

Thanks for replying 🙂 I probably should have added that my hair is more of a brassy yellow than ginger, I tested out a large strand underneath and the colour is pretty much spot on to how I wanted it, however this strand was quite an even colour so it went on well. I'm just not sure that it will go over the darker/lighter bits evenly... Like will I end up with really bright purple roots?

Its currently like this but with some more blonde and mousey bits (I think I've added an attachment but I'm not sure hahah)

Are the darker parts where you had used permanent dyes previously? If so a colour remover will really help.
Getting an even base will ensure an even colour, and most of all an even fade. Deep colours will cover and hide an imperfect base, but you will have to constantly keep the colour topped up to avoid a murky fade.
I have also had the best results with blue toned purples over a pale yellow base, any hint of gold ruins the colour, although other people can get nice purples over a darker base.
I would say don't rush, get your base as even as possible before adding any colour.

If you use Directions Plum on that base it will probably get a warm shade of purple, a bit more on the pink, but it will definitely cover the uneven areas. I have had uneven bleached areas in my hair and once it was dyed, I couldn't notice any differences from the even parts. I'm not sure about the Violet though. I used it a couple of years ago but stopped after the first pot. It looked weak on my hair and seemed to wash away easily.