Look at the diploma sylabuss, which is the next step up from grade 8. There are a lot of difficult pieces on that list which require speed, and are significently more difficult than grade 8, for example Gershwin preludes, or I got rhythm. Also Ravel sonatine has a very fast 3rd mvt. The Bach pieces are very good for speed as well, and helps a lot with mastering music of chopin and Liszt. Once you have reached diploma standered and fell the pieces don;t challenge you tecnically, move onto the LRSM list, which is higher again. On this you will find Chopin Scherzo's, etudes.. Liszt's etudes, Rachmaninoff preludes, and some very fast repertoire.
It takes time to learn to get the speed required for fast virtouso passages, I never really went out of my way to learn to play fast, I just developed through years of Hannon, and Czerny studies. Also my teacher give me pieces which were fast, and then give me faster ones, but very steadily.
The best way I feel to play fast is to completly relax the arms and fingers and just let the notes float of the fingers, and don't actually think I'm playing fast, just concentrate on the relaxation. Play some Chopin preludes, a lot of them are very fast... for example no. 12, and the Bb minor. Also the Dminor for some rapid LH stuff, and some very fast scales and arpeggio's. Also Rachmaninoff's transcription of flight of the bumble bee is very fast.