Northumberland is the least crowded county in England, and that shows in its pony breeding — big hill farms running down from the Cheviots produce genuinely hardy, sensible native and native-cross ponies used to wide open country, real weather and long distances between neighbours. It borders the Scottish Borders, and buyers here often end up widening their search across that border without really noticing, since the pony culture is similar on both sides.
Be prepared for real travel. This is a large, sparsely populated county with slow rural roads, and a viewing near Berwick and one near Hexham can be well over an hour apart. Ponies bred on Northumberland's hill ground are typically excellent all-rounders for a family who hacks out a lot, being sure-footed and unbothered by isolation, weather or livestock — but many are sold with more life experience than schooling, so ask clearly about ridden training.