Thanks ken, I figured about getting caught for it anyway so was trying to work out the final delivered price to see if it even worthwhile buying from japan or just buy from the uk.
Nengun offer 3 options for declared insurance value, you can value it at 100% and get stung for everything or you can value the parts at 10% or 50% in which case customs may only charge you on that 10 or 50%. But the flip side is that if you're package goes missing, you're only insured for the declared value and with parts worth over a grand, I'm not sure it's a chance I'm willing to take.