I called Google CS. It's been six weeks since my faulty phone was collected and shipped back to LG, Poland. Google say it was received 15 March so took 6 weeks (!) I am waiting to hear if they expedite my refund as right now both phones are showing as purchased (or, more bizarrely 'pending') on my account. I kept the replacement phone.
This is what puts me off Google devices, more than anything; the lack of a physical entity to deal with.
Has anyone else in England had this problem?