I had this problem on a 2011 model. If you pull down the roof headlining in the centre, the hose from the washer pump is connected to a shorter length of tube that connects to the washer nozzle in the high level brake light. The coupler is a white fitting about 40mm long and sits in a clip. If you pull off the hose from the washer pump, at the coupler, and try the rear washer, you should get fluid squirting out of it. It's easier to get someone to hold the hose and direct it into a bottle. If it squirts out ok, you know there's not a problem with the pump or hose. The coupler contains what looks like a spring-loaded non return valve. I removed the coupler and pulled out all the bits inside so I was just left with the outer plastic tube. I reconnected the pipes, tried the washer, and it worked. I can only think the non-return valve was kaput and blocking the fluid flow to the nozzle.
Take care when pulling the headlining clips out, try not to bruise the squashy headlining.
