Pre-lightener?

From England,

Hey,
My hair is currently dyed red but has faded to a reddish brown which I like, but now I have mousy brown roots coming through. The 'redness' of my hair is quite patchy due to using different shades of dye and I wondered whether using a pre-lightener before applying the new shade of red dye is a good idea to create an even base?
Any feedback would be appreciated
thanks, jenn