Just to clarify for others reading this thread, simply having too much/heavy luggage
is not an appropriate use of Passenger Assist, and people misusing it just because they have brought too much luggage for them to handle by themselves only makes it more difficult for those who really need it (and may, for example, have hidden disabilities) to get the assistance they require.
However, if you need assistance with reasonable amounts of luggage
because of a medical condition/disability, or would struggle due to old age, then you can request the help of Passenger Assist.
As it has been put in the past:
A family member recently had a issue with a booked "assist" at a London Northwestern station. She was travelling with luggage and a baby in a pram and required help with the luggage whilst changing trains. She was met by two members of station staff on arrival, who took one look at the pram and...
www.railforums.co.uk
Of course, if OP needs a seat due to a medical condition (which they may, as they have mentioned a hospital referral), they are more than welcome to request assistance, and I would echo the suggestions to do so from others in the thread.