If North lakes and near Keswick you can get day membership for Keswick Anglers from the Public Information office in Keswick, giving you access to the river Greta (along A66 near Threlkeld) or river Derwent near the town. Some lovely fishing on both those rivers. Or at Penrith call into John Norris's and you can get Penrith AA tickets for the Lowther and Eamont near the town, or Go Wild vouchers for the wild trout trust scheme for some off the beaten track wild stuff. Loads to go at and very reasonable prices

Can't help you much with south Lakes though I'm afraid, not fished much round there.