Water ingress in boot caused by rear screen washer

I recently noticed that my rear windscreen washer on my 1.6 zetec 04 wasn't working - the pump sounding like it was working but there was no water coming out.
I also noticed that the boot was wet. I got someone to press the rear washer stalk whilst I watched the inside of the boot to see if I could see what was going on. To my surprise I could see water gushing into the boot near where the rear right drivers side brake light cluster is situated. Has anyone had a similar problem, or does anyone know where the source of the leak could be?
Thanks, Rick

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