I have dark brown hair naturally that I colour with a semi permanent dark brown dye every 6 weeks to cover a scattering of grey hairs.
I decided I would like something a bit more exciting like a red colour. Purchased a pemanent 'Garnier 100% color in intense red' and coloured my hair. Its covered my greys and is even all over but my hair is still dark brown with red tones noticeable in daylight. I really wanted something more intense, is there any way this is achievable at home? I would not consider stripping the colour out of my hair first as that just seems too drastic and damaging to the hair. Any tips or ideas would be appreciated.

You'll want to wait at least 2 weeks before doing anything else to your hair. I suggest going to a professional salon and getting it done there, they will be able to tell how your current hair color will mix with the dye in order to achieve the results you want.