Bevan almost succeeded to get on top of mass disorder (8)
I believe the answer is:
aneurism
'on top of mass disorder' is the definition.
I know nothing about this answer so I can't tell whether this works.
'bevan almost succeeded to' is the wordplay.
'bevan' becomes 'aneurin' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'succeeded' becomes 's' (genealogical abbreviation).
'to' becomes 'm' (I am not sure about this - if you are sure you should believe this answer much more).
'aneurin' with its final letter taken away is 'aneuri'.
'aneuri'+'s'+'m'='ANEURISM'
'get' acts as a link.
Can you help me to learn more?
(Another definition for aneurism that I've seen is " Abnormal dilation of an artery".)