Claire Enders, founder and chief executive of Enders Analysis, said the move had come as a surprise given that the grounds for intervention appeared relatively weak.
But she said Nandy, an ally of Andy Burnham, who is set to become Britain's next prime minister this month, appeared to be using the prospect of delay to secure commitments.
"Substance is never that important," she said. "What really matters is making big promises, way in advance of events. And this intervention seems to be structured in order to attain that."
