To register as disabled in the UK, you might want to consider these steps:
Consult your GP or a relevant medical specialist. They can provide medical evidence and support your claims if needed.
Depending on your situation you may be able to apply for certain benefits. If you have mobility issues you can consider applying for a Blue Badge to allow you to park closer to your destination.
If you have a sight or hearing impairment, contact the MK Sensory Service who can provide more information and support.
There are several national schemes which offer disability card registration.
National Disability Card UK ⎜Easy Online Application