Wella Colour Fresh lasts for up to 8 washes (so no peroxide, it doesnt penetrate the hair shaft)
It's not so easy to find as the one you've been using though, as it isn't sold in Superdrug etc. Also quite a bit more expensive I believe
I use it sometimes to change the tone of my hair (which is naturally light blonde) It does wash out fast though, as my hair isn't bleached (about 2 washes as opposed to probably 8 on chemically lightened hair)
You can buy it online, but I get mine (much cheaper) in a shop that sells lots of hairdresser supplies.
Sally's sell it I think, and they have shops.
I wouldn't use anything that said 28 washes on my hair (some people seem to think that if the box says "semi permanent" it will wash out completely, which of course it won't, especially if used repeatedly)