If you want proper cliff tops, you need the Yorkshire coast, rather than Northumberland, which tends to have dunes. You need to watch they don't disappear from under your feet, though. My parents' house is a mile from the coast and, at the current rate, it's got a century at the most before it falls into the sea!
If it swings the distance thing, I found living in the north-east and travelling to parents in the south-east much easier by both train and road than travelling to (now ex-)PIL a shorter distance but cross-country. So either Scottish borders or Northumberland might not take as long as you think. London-Devon takes me longer than London-Newcastle.