At the more expensive end of the market, but worth it if you want to impress. See Article on new city branch. There are two cut flower stalls in the market, one on the corner of Colville Terrace, the other on the corner of Westbourne Park Road. Both offer competitive prices and are there on weekdays, as well as Fridays and Saturdays. The stallholders by Colville Terrace seemed more interested in taking special orders in advance, but that's not to say the others weren't willing to as well.
Prices vary according to the season, but now's the time to buy fantastic tulips.
Useful for last minute panics. Just at the top of the stairs on the Pembridge Road side of NHG there is a kiosk on weekdays.