As I understand it the distinction for dual control cars is that the usual rules about capital allowance percentages for “cars” don’t apply - they’re eligible for Annual Investment Allowance so you can claim the whole cost against tax in a single year. But that’s just for income tax purposes, for your accounts you’d depreciate it normally the same as any other vehicle.
NB I’m not an accountant, check with a real one if you want to be sure.
As these cars are modified for special purpose and are not commonly used as a private motor vehicle hence they qualify for AIA in tax return. Only thing you need to be careful on is the private use, significant private use can reduce tax allowances