Former PM keeping dry in a shelter (6)
I believe the answer is:
attlee
'former pm' is the definition.
(prime minister Clement Attlee)
'dry in a shelter' is the wordplay.
'dry' becomes 'tt' (short for teetotal - no alcohol).
'in' means one lot of letters goes inside another.
'shelter' becomes 'lee' (as in lee side, the side sheltered from wind).
'a'+'lee'='alee'
'tt' going inside 'alee' is 'ATTLEE'.
'keeping' acts as a link.
(Other definitions for attlee that I've seen before include "British premier" , "British PM, 1945-51" , "Labour PM" , "Clement -, UK PM" , "Granny Smiths perhaps" .)