After reading I might need a firmware update to connect my iPhone5C, I spoke to a South East London VW dealer who wanted over £100 just to do diagnostics on my RCD310 to see if I needed the update
Also, they would only do so on certain days of the week.
Decided to order a genuine VW cable on-line and test for myself. Worked first time
Anyway, reason for the post: I bought it from a German dealer called Autohaus Koller , via Amazon.co.uk
It was £38 plus £12 P&P which I thought was steep, until it arrived under 36 hours after placing the order. Or about the same time it took said dealer to return my initial phone call
Awesome service from Autohaus Koller
