YA novel that I read in 1987 at school - two young British guys captured by terrorists and escape from a pit

Question

In 1987 I began high school. There was one YA novel that the school librarian put on a special part of the shelf because it was "too frightening". If this was reverse psychology it worked because I borrowed it. I cannot recall the title. I didn't finish it. I got about 1/3rd of the way through/skimmed some of it/jumped to the ending. Anyway:

1. It was set in England. It had a British author.
2. The front cover showed a boy crawling out of a pit with a terrified expression.
3. The plot was that two young British guys - teenagers - went around Britain tandem on one motorbike. They stopped at a beach and stumbled on a terrorist camp. One of the terrorists knocks them both out with rocks. They wake up in a cave tied to a bomb. They are told that a terrorist plot is going to happen in a week where bombs will be put on British boats and subs at UK ports to blow them up and hurt the British government. They are allowed to live until the plot is done.
4. Then I skimmed/skipped [maybe the due date got close] and the final pages had one of the teenage captives escaping and climbing out of a pit like the front cover. He passes quasi supernatural beings real and/or imagined.

I have tried various book forums. No suggestion has been it. It was very well written. For instance when the guys get captured there is a two page description of the pain of being hit. It's a bit synesthesia like with pain being a colour. I wouldn't mind reading it again or seeing what else the author did. I feel that it was a male author.

This is a tough one. I don't really expect an answer; I've given as much detail as I honestly can.

Answer 1

No idea why I hadn't seen your post before; I recognised the story instantly from your description, and for some reason it stuck very vividly in my mind both when I first read it as a child and when I reread it as a teenager.

This is almost certainly Annerton Pit by Peter Dickinson.

The only detail that I'm surprised you missed or forgot is that the main character is blind (the younger of the two boys). If this too rings a bell, then I'm absolutely certain it was Annerton Pit that you read.

The boys are Jake and Martin, two brothers. Martin is around 18; Jake is younger, maybe around 13, and blind. (One of the most memorable things about this book for me, especially on second reading, was its convincing portrayal of life as a blind person. Sometimes I would come away from the book after some chapters and feel that I too needed to rely on my non-sight senses to get around.) They go on a motorbike together in search of their missing grandfather, who is interested in the supernatural.

Eventually they trace him to an old mine in the north of England (Yorkshire?): the titular "Annerton Pit". But they find that a group of terrorists has kidnapped their grandfather, and proceed to capture the boys too, because they're using the mine as their headquarters and don't want their plans to be discovered. The trio are initially kept in a caravan, but later they escape (?) to the mine tunnels underground. The boys' grandfather is in bad health and they fear for his life. At the end of the story, they escape through the tunnels, and one of the terrorists

blows up the mine with himself inside, to avoid being taken by the police. This man had previously told the boys something like "I was told that you're really committed to a cause when you're willing to die for it, but now I learned that you're really committed to a cause when you're willing to kill for it". At the end of the book is the line "[Name], unable to kill for his cause, had deliberately died for it."

There is also a supernatural angle. Annerton Pit was closed years before due to a mining disaster where many people died, and there was speculation about a creature living underground, which is what led the boys' grandfather there in the first place. Towards the end of the story,

Jake, crawling blindly through the tunnels, feels a presence there with him. I think he even communicates with it somehow.

Searching online for cover images, I can't find the one from the edition I read (which was more realistic/"photographic" in style), but here's one which matches your description: