if you travel with a disability, you may require some assistance when you travel. I've never booked assistance to catch a train; but have had to book assistance for catching a plane.
I contacted Flybe (how to do this is on their website) with a brief description of my needs, flight details (just time, date where from and to) and my disability. They sent me a confirmation email of this. I'm ok checking in; it's the getting around the airport safely that's the problem and finding the right gate. After showing my passport to check in, the person at the desk tells me they'll get someone to help me through security and get on the plane. I've only ever flown with Flybe and have never had a problem at all with the assistance I've received.
You'll require travel insurance. Depending on your situation, you may have to pay slightly more. Shop around. I, for example, get it free with my bank; but had quotes up to £300.