After checking all the door, boot, light seals, rubber gromits from the collision bulkhead, intercooler water spray line. I lifted the front footwell carpets to find that there were 2 small holes in each front wheel arch where someone had previously removed mudflaps. With the carpets lifted you could clearly see that water and dirt had been coming in through the holes.
Stuck some silicone in them and dried the carpets out with the missus' hairdryer and all looks good.
Hopefully this has cured the problem