So my sister has bought a Ka! Its a 2006 Design, for which she paid £800 with a new clutch and not a spec of rust (had it properly inspected on a ramp) from the bloke who lives opposite. Going to help her install a bluetooth radio next weekend, basically just looking for suggestions on which ones best and where I can get the fascia and ISO adapter things. Also, the installation video on Youtube is a bit unclear so if anyone knows of a better guide let me know.

Personally, I'd recommend a Sony radio system with BT and USB. I had a few Sony head units installed in various vehicles. 
I picked up the fascia and all wiring adaptors from Halfords and it was a simple case of plug and play. 

Brilliant, any ideas of rough cost?

The fascia for the ford Ka (96-08) is £11 from Halfords.
The ISO harness is £12 from Halfords. 
Sony BT/USB head units start from around £69 (currently 20% off certain stereos) from Halfords. 
A stereo upgrade could cost less than £100 if DAB antenna and steering wheel controls are not needed. 

Great thanks, DAB not needed and does the MK1 Ka even have steering controls?

 

maybe not in an 06 one so you should be fine. 
Any wiring loom needed will just be plug and play so easy to fit (no splicing etc required). 

Brill, was really easy fitting mine to my Focus as the previous owner had already done all the adapters and things. I just had to take the old one out and push it in. One question, in this video:

What is the bloke doing with folding the pins in the cage. I can’t make it out properly and he doesn’t explain it very clearly. 

1 hour ago, dtulip8 said:

What is the bloke doing with folding the pins in the cage. I can’t make it out properly and he doesn’t explain it very clearly. 

He's folding the little metal retaining pins so that the radio won't slide out either when braking harshly or if someone tries to steal the unit. If you do that, the only way to get the radio out is to remove the whole fascia. 

Ah so I won’t need to worry about doing that then?