My car, although not quite a tank, is 2.1m wide and the garage is currently 2.7m. A minimum of 1.4m of door opening space seems to be recommended i.e. 80cm for driver + 60cm for passenger side, hence 3.5m as a target.
I've attached the layout for the ground and first floor and have added a red box for the most simplest extension. Bedroom five above the garage doesn't go out to the full width - looks about 3/4.
It also needs lengthening by 2m. Doing this outward will just bring me to the 45 degree rule for neighbours window, but happy to sacrifice the pantry if needed as I'll be looking to extend and remodel the ground floor.
There is also an option of sacrificing the WC by the entrance and extending inwards, but this will be more complicated.
I hadn't considered a car port, aside from how it'd look on that road, bedroom five above may be tricky. But it'd certainly remove the need for a brick wall extension and so provide some extra space...interesting idea.