First day of the Triffids

We have been in our house for just over 5 years now. Half way up the end of the garden is a spiky plant. Nothing exciting, just green and spiky. Didn't do anything, but be green and spiky. Then in the last month a giant stalk, like a huge piece of asparagus, grew up out of it. Now its starting to look like its going to flower sometime soon.

Its not a good pic, but I'm guessing I'll take a few more when the flowers come out and I wanted to get the whole plant in (while not showing the falling down fence)

Any ideas on what it is and how often it flowers would be greatly appreciated.