We really know little about the Iberians (besides some "stories" of fairies, brownies, and "little people."
But they have created Stonehenge, it seems.
Negelcted in history books is as well the invasions of the Scots and Welsh people to England before the Celts arrived.
You can find some (more) mentions about the Jutes, when you use e.g.
Google print and/or
Google scholar.