Maybe you just have buyers' jitters and it will all be fine See how you go first. If valuation is a problem then maybe you should go with a lender that doesn't even do a valuation.
Aaron's sane words helped and surprisingly it was a storm in a tea cup. We (REAs, myself and broker) were all prepared for the worst and today the Valuer has sent the valuation in and agreed with sale price. The non comparables were sorted by providing comparables with houses on and deducting the price/value of the house/improvements.
It's gone off to Mortgage Insurers for next stage of approvals.
As per usual - thanks for your wise words of wisdom boys.