Taken from the National Rail enquiries webpage;

Travel Assistance
Do you need any extra help traveling by train?  Here is a quick guide of what you can expect from all train companies as a customer with a disability.
Helping you with your journey
You can book to get help at any station for any train journey.

The train company can organise for someone to:                                                       

• meet you at the entrance or meeting point and accompany you to your train
• provide a ramp on and off your train if you need one
• meet you from your train and take you to your next train or the exit
• carry your bag (up to three items of luggage as per the National Rail Conditions of Travel

You can book help at short notice.  Some companies may ask for up to 24 hours’ notice.

Rail services are now far more accessible than they were in the past and many disabled people are able to use the rail network without assistance.

Staff will help you if they can, even if you just turn up.  Sometimes this might take a bit of time because staff will have other things to do, like dispatch a train or look after safety on the platform. If staff are not able to help you they will explain clearly why not.

...

Throughout your journey
• The train company will do all it can to communicate with you in a way you can understand
• Staff will treat you with respect and dignity
• Staff will understand your needs as a customer with a disability
• Trained staff will know how to use any company equipment that will help you with your journey.

It looks great but Northern don't subscribe to this policy, despite it being a national rail policy, actually a fair and reasonable expectation of their staff and required by law.