Help with getting rid of dandruff without stripping colour?

try Paul Mitchell's Tea Tree Special Shampoo. It's a clarifying shampoo but it is also color safe.

Was it bleached?  I always get dandruff when I bleach my hair but it goes away.

You could try a leave-in scalp treatment instead of a dandruff shampoo.  I use Avon's oxygenating scalp treatment, and it works really well for me.
http://avonshop.co.uk/product/haircare/treatment/advance-techniques-keep-clear-oxygenating-scalp-treatment.html

There's a scalp treatment at Lush called snake oil that helps ease scalp irritation / dandruff issues 🙂 it's a solid bar so you just rub it with your fingers and apply directly to scalp, I think you can leave it on until your next wash.
http://www.lush.co.uk/shop/product/product/path/147_151/id/384/handmade-hair-hair-treatments-snake-oil

And it will last aaaages 🙂

His hair was only bleached where the purple went in, so a small slice, but his whole head is dandruffy.

Mindi - Thanks for the link, that stuff looks great - will give it a go.  😀

Violet - Again thanks - I do love Lush's products and used to use them regularly but had to stop supporting and buying from them on principle when they launched their moronic 'Reptile keepers are cruel animal murderers' in conjunction with the APA last year.  🙁

I have just noticed you're from Gloucester? So am I! 🙂 I work at Lush in Cheltenham.. and was in the paper for that bloody campaign (even though I only work there one day a week now and knew hardly anything about it! Mayhem.) Anyway; It's good stuff though, if you change your mind pop in and I'll get you a big cheeky sample just to see how your partner gets on with it, then hopefully you won't have to buy it.