If you are heading to the Lake District I've been informed by a National Park Ranger that you can fish Styhead Tarn with just a rod licence, no need for a permit. And having spent quite a few evenings there it's heaving with trout.
There are also fish in the tarn below the summit of Helvellyn, Red Tarn IIRC. Again no permit needed, so I have been told.
Both are beautiful places to be even without the fishing.
Another place that doesn't require a permit is the Upper Derwent River, between Derwent Water and Borrowdale, and if you see it say hello to the big fat brown trout I spent two years trying to catch!!
"Experience is not what happens to you; it's what you do with what happens to you." Aldous Huxley