British YA/older children's thriller book I read in the 90s - kid(s), murderer(s), and a dead body in an ice cream van

Basically as the title says.

I read this book in the early 90s. It's from the UK, there's at least one kid, a dead body is discovered in an ice cream van, and a cat-and-mouse plays out between the kid(s) and the murderer(s). I think maybe a kid finds the body, tells the authorities, and they go and search the van and find nothing - but the killer(s) are now on the trail of the kid to shut him up.

That's all I've got! I have no further info, but I'll know it when I see it. Thanks in advance for any help.