It is a Globe Artichoke that has run to seed!

See here;http://www.thegardenersalmanac.co.uk/Data/Globe%20Artichoke/Globe%20Artichoke.htm

It's a Cardoon or Cynara cardunculus. Also known as globe artichoke as mentioned.

Your photo shows the flower.

They can get huge, ive got them to about 8-10 feet and certainly 8 feet across. Oh...and blackfly love em !!!!

They taste lovely too.

When this thistle like head goes to seed completely it is edible when prepared by trimming and then boiled. The scales can then be eaten at the base...nice dipped in butter. Also base of the 'choke can be eaten too. They are sold tinned and the whole vegetable sold in season in most supermarkets and at posh veggie stalls.