About replacing a Nexus 4...

I bought it from the Carphone Warehouse... So would I be trying to get a replacement from them? Or sending it to Google or LG? Because of the time Google or LG would take a really can't be arsed to send it back if that's the case. Of course, if it's the Carphone Warehouse I can just pop in and swap it.

The reason I want to replace it is because of a HUGE amount of dust under the front-facing camera. I can barely see the lens through it and couldn't get a decent picture, but this is what pictures look like with it:



Compared to:



I don't think the dust was there when it arrived, and I haven't been using a screen protector. Do I have a claim for a free replacement, and if so, from whom should I get it?