Mediterranean bill, abruptly raised by British politician (6)

'british politician' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'mediterranean bill abruptly raised' is the wordplay.
'mediterranean' becomes 'med' (short for Mediterranean Sea).
'bill abruptly' becomes 'bil' (I am not sure about this - if you are sure you should believe this answer much more).
'raised' shows that the letters should be reversed in order (going up in a down clue).
'med'+'bil'='medbil'
'medbil' reversed gives 'LIBDEM'.

'by' acts as a link.

Can you help me to learn more?