I've literally just done this...after hunting down Chris's thread from last year!
This is the adapter he is talking about:
£6.99 from Maplin...
CLICKY
As Chris says...drivers side lower dash off (6-7 torx screws), which will reveal the power dist block under the steering wheel.
Chop the adapter plug off the 4-way jobby, and then crimp spades / Orings crimps on.
The wire with the white tracer is the +itive.
With a little pushing & squeezing the 4-way fits into the slot under the steering wheel where the Owners Manual normally fits...
Here's a pic installed:
Thats my Brodit phone charger plugged in but TomTom and anything else is dead easy to do...as you can imagine!
Took me about 30mins all told...shout if you want a hand...