Thanks LLF64 and The Boy,for your advise.
My plan ,after reading the notes re stepped down voltage ,is to buy a retro fit female ciggy lighter lead.Hard wire that into a live feed ignition switched wire and an earth ,and then mount the housing above the footwell area of the passenger side centre console.That will then allow for the Tomtom power cable to be plugged directly in without disrupting any circuit boards etc.
I will then feed the usb end,as suggested up behind the centre wood effect console and bring it out around the opassenger side centre air vent.It was then my intention to buy a satnav air vent mount so the unit is in the middle of the car, but not screen mounted as I think it looks too taxi like,hopefully giving a tidy and practical installation without too much grief.
Am sure I have read somewhere that you can buy units which allow Tomtom satnavs to be placed in almost like a phone base charger and then lifted off when you need without the need to remove plugs etc..has anybody had any experience of this type?.
Any other fitting advise greatly appreciated ,before I attempt the above.