All the London railway stations :
Euston is accessible to wheelchair travellers in the National Rail station, but limited access to the Underground stations. See pictures and further accessible transport in London detail from links below.
Underground lines : Northern, Victoria, London Overground (Watford DC Line)
Accessibility friendly : Partial. No entrance/exit on Underground. You can change between Victoria line southbound towards Brixton (A step 50mm/gap 75mm) and Northern line southbound towards Morden via London Bridge (A step 147mm/gap 0mm).
You can change between Victoria line northbound towards Tottenham Hale (A step 50mm/gap 75mm) and Northern line northbound (Bank branch) towards Camden Town (A step 160mm/gap 0mm).
No stair free entrance to the Northern line Charing Cross
Escalator access between street and platform to Northern line (Bank branch) and Victoria line platforms.
Level interchange between the Northern line northbound platform (Bank branch) towards Camden Town and Victoria line northbound towards Tottenham Hale. Level interchange between the Northern line southbound towards Morden via London Bridge and Victoria line southbound towards Brixton. -
General description : See the Access guide for more detail about Euston station. See wiki
More comment : Step-free access from station entrance to and between National Rail platforms only (TFL)
National Rail Map & Guide, The entire National Rail system is step free, although mainly via ramps.
Inclusive Britain Underground Station Guide