Thank you My Lord, My concern was, as you rightly say, drilling into something the other side that may either lead to a blind cavity or destroying something important (and/or) expensive.
Have run many cables over the years but those vehicles had engine compartments with plenty of elbow room where you could hold a party with your mates (think MGB, Triumph Herald/Spitfire?GT6, Sunbeam Rapier) and you will appreciate my concern that I find it rather difficult to get my hands into a Jazz's engine compartment, let alone stick my head in for a dekko!
Have already run the cables into the engine bay, but after looking underneath expecting to see the underside of the engine, transmission etc. I was somewhat befuddled to only see under-tray as far as the eye could see, from front bumper to some way half way down towards the back bumper. O.K. so I exaggerate slightly, but basically I would like to do as little dismantling as possible due to age catching me up (had classic minis before they were considered classic) and the only flexible joints I have exists on my car.
Will have another look at the inside of a front wing but using a bright torch this time might help.
Thanks for the pointers.
(P.S. Have already been on to Wallace and ordered a box of Wensleydale).