Google help with esa 50 and look for kitty Jones WordPress or black triangle campaign.
They have draft letters you can print off for your Gp.
Also use the terms repeatedly, reliably and safely when describing the descriptors that affect your health.
Lord Freud and Mark Hoban have both stated that if you cannot do the descriptor, repeatedly, reliably and safely, then you cannot do the descriptor at all.
There are also special regulations that basically say you cannot be found fit for work if the work will make
your condition worse. Please see the above sites for more info.
All the Best