UPDATE! OK so after thinking long and hard about the many different ways to achieve Bluetooth music and calls in the car I took a bit of a different option (and a lot cheaper) and am very pleased with the result. The whole install cost me less than £20 and only took 30 mins.
I decided to just go for universal bluetooth receiver but there are a lot of rubbish ones out there. After spending a lot of time reading reviews I went for this for £11.99...
https://www.amazon.co.uk/gp/product/B078W1HQCK/ref=oh_aui_detailpage_o01_s00?ie=UTF8&th=1
To power it (didn't want my ashtray permamently open) I also went for a hard wired 12V to 5V converter (£7.99)...
https://www.amazon.co.uk/gp/product/B07169FM6H/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1
The converter seems to be unavailable now unfortunately but there are loads of similar ones on Ebay.
The install is very simple....
1. Drop the glove box down by pressing the two plastic tabs at the top to reveal the fusebox...
2. Any of the three 5A fuses on the bottom row on the right are switched ignition so are suitable. I already had a piggyback fuse connector in my garage so used this to take the feed from the rightmost 5A fuse...
3. There is a really nice covenient earth point in the form of the crosshead screw immediately below the 5A fuses, but as the original screw is treated you need to either remove the coating on the underside of the screw with a dremmel or use a different screw like a stainless one.
4. Next I dropped the lower kick panel in the passenger side by removing two screws..
5. The DC-DC converter has a USB socket so the Bluetooth adapter simply plugs in. The power wire needs to be fed from the drivers side through towards the fuse box. Luckily there is an easy access route but you need to tape the wire to something quite rigid to feed it through...
6. Once fed through, the wire appears under the fuse box (you can see the resonator tube from the engine compartment in the pic also)
7. Bring the wire up through the gap at the bottom of the fusebox. You then need to terminate the wires with a bullet crimp (+ve) and an M4 ring crimp (-ve)
