Any change in level can prevent independent access in a wheelchair or scooter: there is a wide choice of wheelchair and scooter ramps available to solve this problem wherever it occurs.
What length ramp do you need?
For fixed concrete ramps, Building Regulations would generally suggest a gradient of 1 in 15 (eg: a 5 cm height would require a 75 cm ramp).
However, this is a guideline, and not a legal requirement. If space permits, this is the ideal gradient, but often the height that needs to be bridged is too great to allow such a length, particularly on narrow footpaths etc.