Firm support in emergency meeting (5)
I believe the answer is:
cobra
'emergency meeting' is the definition.
(UK abbreviation for Cabinet Office Briefing Room A)
'firm support' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'support' becomes 'bra' (a support for the breasts).
'co'+'bra'='COBRA'
'in' acts as a link.
(Other definitions for cobra that I've seen before include "Sinuous creature" , "Venomous hooded snake" , "Type of snake" , "Reptile (found in Cabinet Office Briefing Room A?)" , "government emergency committee?" .)