Third party cover will protect British bloke from claims in the end (3,4)

'third' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'cover will protect british bloke from claims in the end' is the wordplay.
'cover' becomes 'lid' (lid is a kind of cover).
'will protect' indicates putting letters inside (inserted letters are held or protected).
'british' becomes 'b' (abbreviation e.g. in BBC).
'in the end' says to take the final letters.
The final letters of 'bloke from claims' are 'ems'.
'lid' enclosing 'b' is 'libd'.
'libd'+'ems'='LIB DEMS'

'party' acts as a link.

Can you help me to learn more?