Just in case anyone has the same problem I found Wella Perfection by Color Fresh Semi Permanent.
You dilute it (measure in cap) and rinse hair with it after shampoo and towel dry but do not rinse it out.
I got the brown but it comes in a few colours and has blended my grey quite well. It is £29.99 on Amazon but can get it cheaper elsewhere and it lasts about 5 washes but the bottle will last a long time as you only need a small amount.
It is a bit like the John Frieda Deeply Brunette type thing or colour depositig shampoo/conditioner.
The first time I got my husband to do it over the sink and the second time I did it in the shower but next time I think I will just put the shampoo on and when it is lathered up add it and leave whilst getting showered and then rinse off and see how that is.
Anyway, I just wanted to share if anyone wants to go grey but blend the badger stripe and hope it helps someone.