They say the lives of 20,000 people could be in danger if there is a fire at either of the terminals - to be built four miles apart at South Hook and Waterson - or on a ship bringing the gas to them.
Lord Justice Keene concluded that legal objection to the plans had been brought outside strict time limits which govern such cases, and added that even if the 'delay' was ignored, there was no public safety issue.
But objectors' lawyers say it has now emerged that evidence both the Court of Appeal and the High Court relied upon from the Health and Safety Executive (HSE) was 'misleading'.
Barrister David Wolfe, for the campaigners, said that in earlier written submissions, the HSE had stated that a risk assessment had been carried out on the potential danger of a fire on a storage tanker.
However, it has since become clear that statement was inaccurate, and there was no such risk assessment, Mr Wolfe told the Appeal Court today.
The barrister said that, although work on the assessment had started, it had never been completed and there was a danger of a 'real injustice' having been done.
Arguing the supposed risk assessment was a 'crucial' piece of the 'jigsaw' in support of the plans - which will cost hundreds of millions of pounds to bring to fruition - Mr Wolfe urged the same three judges who heard the earlier appeal to reconsider their decision.
'Once that piece of the jigsaw falls away, it is no longer sustainable,' he said.
Earlier Lord Justice Chadwick had rejected arguments made by Mr Wolfe that a differently constituted Appeal Court panel should hear the case.
He argued that, if Lord Justice Chadwick, Lord Justice Keene and Sir Peter reconsidered a case they had already rejected, there might be an 'appearance of bias'.
However, Lord Justice Chadwick dismissed the rarely seen application for the judges to 'recuse' themselves from hearing the case.
The court has heard local people are worried that, if there is an explosion or a fire at either of the terminals or on large tankers bringing gas to the plants, thousands could be killed.
Mr Wolfe said a highly inflammable cloud several miles long could occur, and it would be capable of engulfing a large area, including settlements within four miles of the proposed terminals.
At the Court of Appeal, campaigners said not only were the proposals unsafe, they were a violation of Article 2 of the Human Rights Act, which enshrines the 'right to life'.
If the scheme were knocked back now, it would cost millions of pounds as preparation for the first two phases of building work at the terminals has already begun.
The case is being brought against Pembrokeshire County Council and the Pembrokeshire Coast National Park Authority, both of whom approved the scheme.
Given its importance, the Appeal Court judges have reserved their decision on the re-opened appeal and will now give their ruling at a later, unspecified, date.
STRAND NEWS SERVICE