The disabled badge scheme applies only to the on-street parking. The disabled people are allowed to park on yellow lines. In England and Wales, they are allowed to park for three hours whereas in Scotland, there is no time limit. If you are in a place where there is a time limit, then it is advised that you should display the blue badge as well as the blue parking clock which shows the time of your arrival. The time clock should only be displayed when you have parked your car on a yellow line or in those Blue Badge parking bays that have a time limit. 
The disabled badge holders are allowed to park for free at on-street parking meters and the pay-and-display machines, for as long as they need to.
The disabled badge scheme however does not apply to parking on off-street, private roads and at most airports.
Always place the disabled badge on the dashboard of the car so that it can be seen clearly through the windscreen. Make sure that the front of the badge is facing upwards and the wheelchair symbol is clearly showing. When the badge holder is not using any parking concessions, the disabled badge should be put out of the view.
In England, the disabled badge holders are exempted from paying the London Congestion Charge. But registration has to be done with Transport for London at least ten days before the journey. Its registration fee is £10. Disabled badge holders are also exempted from tolls at certain river crossings, bridges and tunnels.
In case an enforcement officer – a police officer, a traffic warden, a local authority parking attendant, or a civil enforcement officer – wants to inspect someone’s badge, then they should let them do so, otherwise they might be fined.
Disabled badge holders are not allowed to misuse their badges. If they are found doing so, then the local councils can take away the badge. Some of the misuses are allowing other people to use the badge, or if the badge holder is a passenger in a car trip, then letting the driver take the benefit of free parking.
For getting a blue badge, an assessment needs to be done to make sure that the person who really needs one is getting it.
There are certain cases in which assessment is not done. These cases are someone who is registered blind, someone who has received a higher rate of mobility component of Disability Living Allowance, and someone who has received a War Pensioner's Mobility Supplement.
Moreover, a person is eligible for a badge without assessment, if they have a permanent, substantial disability which makes them unable to walk or walk but with very difficulties. Also those people are eligible too who have a severe disability in both their arms and they find it very difficult to operate parking meters.
Furthermore, a person can apply for a disabled badge if they have a child who has certain medical conditions which forces them to be always accompanied with bulky medical equipment which have to be kept close to the vehicle at all times, so that in case of emergency the child can be treated in the vehicle, or can be quickly driven to a hospital for treatment.
If these conditions do not apply to some applying for a blue badge, then an assessment is necessary. The council will ask questions so that they can decide whether or not the person is eligible for a disabled badge. The council can also get information from the doctor, or ask to see an independent health professional.
Disabled badges are for facilitating the disabled people, so this facility should not be misused by others.