Mini Clubman 1100 with a 2.5" Cherry bomb, could be heard 2 miles away (as my mate told me when he heard me driving down!)
PCN - Penalty Charge Notice for parking - not sure why a CB would attract one!
Any modification that increases the noise from the exhaust is strictly illegal. (section 59 Construction and use regs)
To fit a CB to a Foz would involve welding the CB in in place of the stock rear box, so unless you can weld, don't bother!
Simon