The mk2 focus has a fused 12v positive in the boot behind the drivers side panel in the boot,
The mk6 fiesta also has this.
Its for a 12v socket but would power an amp nicely.
I know yours is a mk1 but it could have it,
Great if it did.
But if not,
Then Id run the cable inside the car behind panels and through a grommet in the firewall,
Also run the power cable and audio cable on opposite sides of the car.
If you run the power and audio next to each other it will cause interference on the sub
It doesn't seem that there is a rear output that I could plug into unfortunatly. Is there any particular place in the firewall you would reccomend? I have noticed that a number of folks in the US have poked a hole through the firewall where the steering column exists. I guess this would be ok though the cable would ahve to go all the way over the other side of the car.