The BBC has a video article on the re-introduction of Cranes to the south west of England courtesy of eggs from Germany. Apparently these massive, leggy birds with an eight foot wingspan were common in Britain up until 400 years ago. Wikipedia has an interesting though slightly inconclusive page on the history of Cranes in Britain including their slow reappearance over the last few decades – both naturally and via deliberate reintroduction. What's not clear is why they vanished four centuries ago, but I presume they were hunted and eaten!

The fact that Grey herons are sometimes referred to as Cranes, especially in rural parts of the country is responsible for the some of the historical uncertainty it seems. They are obviously fairly similar, though Cranes are rather larger and more exotic in appearance. I've not seen one myself, but if I wanted to then Norfolk is the best place to do so at the moment with a small breeding colony numbering only about 20 individuals.