What is this plant? I love it!

Can anybody help? 

My neighbour has this plant growing over there fence in to our joint pathway and I really like it! 

Does anybody know what it is? I have asked my neighbour but the plants were already established when they moved in so they do not have any idea either. 

The flowers are really pretty but only come out early in the year then fall away. 

Any ideas would be very helpful as u want to get a few for my fence. 

Grahame