Fight here if held up by British PM or ignored by Lord (11)
I believe the answer is:
battlefield
'fight here if held up by british pm or ignored by lord' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'fight here if held up by' is the wordplay.
'fight' becomes 'battle' (synonyms).
'here' becomes 'eld' (I can't explain this - if you can you should believe this answer much more).
'held up' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'if' reversed gives 'fi'.
'eld' after 'fi' is 'field'.
'battle'+'field'='BATTLEFIELD'
Can you help me to learn more?
(Other definitions for battlefield that I've seen before include "Scene of military action" , "Scene of conflict" , "arena" , "situation demanding firepower" , "Place of conflict" .)