All the London railway stations :
Elephant & Castle is on the Northern and bakerloo underground lines, and is largely not accessible to wheelchair travellers between street level and platforms. There is lift access between street and southbound Northern line platform ONLY. See pictures and further accessible transport in London detail from links below.
Underground lines : Northern, Bakerloo, National Rail First Capital Connect
Accessibility friendly : No. You can only enter and exit the Northern line southbound platform for trains towards Morden (A step 183mm/ gap 3mm).
Lift access between street and southbound Northern line platform ONLY, towards Morden.
General description : See wiki
More comment : Inclusive Britain Station Guide