It’s a good idea to have a car to explore Northumberland. The M1/A1 takes you right through the area and is a perfect artery to explore from. It is widely accepted that getting around Northumberland by car is far easier than its neighbours, meaning less time travelling between locations.
Alternatively take the fast train in less than 3 hours from London King's Cross to Newcastle, Alnmouth or Berwick-upon-Tweed. Buy tickets from The Trainline.com, the UKs leading seller of train tickets online to all UK mainland destinations.
There are countless flights to Newcastle from many cities in the UK. Check low cost airline deals to Newcastle with Lastminute.com. Once there you’ll probably look to hire a car.