What was that programme/s called in the 80's on (school holidays))

All i can remember about this programme is that there were these two boys who were on a school trip or something and they went into the woods to explore and they get captured by to tramps and in the end they use a magnifine gl to make fire and get help... now wasnt sure if it was bbc2 or chan 4 who aired this programme.. they also did several others programmes like these and i loved them... ne one help