British action wouldn't have mattered.
( ( British action ) ( ( ( would n't ) ( have mattered ) ) . ) )
(ROOT (S (NP (JJ British) (NN action)) (VP (MD would) (RB n't) (VP (VB have) (VP (VBN mattered)))) (. .)))
British action would have made a big difference.
( ( British action ) ( ( would ( have ( made ( a ( big difference ) ) ) ) ) . ) )
(ROOT (S (NP (JJ British) (NN action)) (VP (MD would) (VP (VB have) (VP (VBN made) (NP (DT a) (JJ big) (NN difference))))) (. .)))