Sir Keir Starmer, the Prime Minister, and Mr Miliband previously vowed not to grant any new oil and gas licences if they won power in July’s election.
The review has prompted the Offshore Petroleum Regulator for Environment and Decommissioning, which handles development applications, to impose a temporary moratorium on applications that are already in motion as well, NEO Energy said.
The company said that combined with the harsher tax environment, this had implications for investment.
It added: “Against this uncertain backdrop, NEO and its owner HitecVision have taken the decision to materially slow down investment activities across all development assets in its portfolio.
“In relation to the Buchan Horst project, NEO awaits clarity regarding the UK regulatory and fiscal framework so that the full impact can be assessed.
“This will inevitably delay first oil timing in relation to the project which was previously forecast to be late 2027.”
Offshore Energy UK, which represents developers, has urged ministers to speed up the Energy Department consultation.
In a separate report published on Monday, the lobby group warned Labour’s tax raid on UK oil and gas companies would drive investment overseas and cost the country £13bn.
It said plans to further increase the windfall tax on oil and gas profits and scrap tax breaks would virtually halt all further investment into the North Sea.
New levies drawn up by Ms Reeves and Mr Miliband will result in North Sea oil and gas producers paying 78pc tax on profits from November, the highest rate of any UK industry.
Meanwhile, the landmark decision by the Supreme Court in June has dealt another blow to the industry. It ruled that emissions from burning fossil fuels must be considered when approving new drilling sites.
Greenpeace and fellow climate campaign group Uplift subsequently secured judicial reviews of oil licences already issued by regulators, including the North Sea Transition Authority, which approved Rosebank and Jackdaw and is ultimately overseen by Mr Miliband’s department.