Adaptations are generally divided into 2 categories, minor and major. Minor adaptations include grab rails, door entry systems, and easier handles for windows and doors. Major adaptations include wet rooms, ramps and automatic door openers.
Landlords in the private sector have a duty to make reasonable adjustments, which applies to making certain changes in your home when requested. However they are not required to alter or remove physical features, which includes most major adaptations. For such adaptations, landlords may or may not provide permission. Where you rent from housing associations, these may have specific policies on providing permission for adaptations.
Landlords are not required to fund adaptations. However, you can apply for the Disabled Facilities Grant which will cover up to £30,000 of cost. To qualify for an DFG, both you and the landlord are required to issue a statement of intent to the council that they intend to let the property to you for at least 5 years.
If a landlord provides permission for adaptations, this often comes with a requirement to restore the property to its original condition when you leave.
For more information visit www.equalityhumanrights.com
Or visit www.citizensadvice.org.uk
Good practice guidance for private sector landlords can be found here https://www.nrla.org.uk/resources/looking-after-your-property/adaptations