Those aren't stickers in the conventional sense, they are tampo printed like on die-cast Hot Wheels and Matchbox cars. You can rub them off with a cotton bud dipped in cellulose thinners (there have been posts on SF that recommend meths although I haven't tried it). Best to dissassemble the car first to avoid any risk of the vapour fogging the clear plastic glass.
Unfortunately some of the decoration on Hornby cars occasionally appears to be spray painted - sometimes it's a white sprayed base with the tampo on top of it so that the tampo comes off quickly but the spraypaint needs proper sanding or stripping. It's very difficult to tell before you attack it with the thinners!
Coop