The New English Library churned out loads of paperback fiction titles in the 1970s. One of the biker ones, 'Angel Alone', was even set in my home town of Glasgow, which I found quite exciting at the time. I remember buying a few, including both of these ones I'm ashamed to say.
They were pretty basic exploitation novels; about the war, skinheads, football hooligans, Hells Angels, the occult, Satanists, whatever. I quite liked the gritty style of the pictures on the front covers. Some of the bikes were extremely odd choices though, like the Vincent in the first one above.
In going through some boxes of books recently I came across about a dozen of them. They’re still awful, but they seem quite popular on eBay at the minute so that’s where they’re headed.