Andy Meader, director at consultancy Pegasus Group, told the summit that "we are in a different situation" from ten or five years ago in relation to the green belt.
"Exceptional circumstances or very special circumstances for green belt changes still need to be proven, but you have a lot of authorities that, going back a little while ago, had alternative options," he said.
"They could have other sites developed, whether brownfield or greenfield, before turning to the green belt sites."
"In more and more situations now, as local authorities come to review their local plans, those alternative options aren’t available," Meader said.
"As a result, you are having situations now where exceptional circumstances are present, that wouldn’t have been a little while ago."
Meader said it was "vital" for planners involved in green belt policy to understand the political dynamics of the situation.
He said: "It is vital when preparing local plans or representing developers or objection groups that you get a real understanding of that political situation, because it's only once you’ve really understood that, that you can start to affect the council's decision and go into the situation with your eyes open."
Citing the stipulation in the National Planning Policy Framework that local authorities should be able to demonstrate that green belt boundaries will not need to be altered at the end of the plan period, Meader also predicted that councils would come under increasing pressure to designate 'safeguarded land'.
Such land is removed from the green belt for long-term development needs beyond the plan period, in addition to green belt sites that are allocated for development in local plans.
"A lot of local plan inspectors are taking the view with safeguarded land that they are not pushing for it too hard," he said.
"I think that could change a bit. I think there could be a bit more pressure to identify safeguarded land."
Guildford Borough Council recently adopted a local plan which provided for land releases from the green belt to help meet development needs.
And Rugby Borough Council's local plan, which proposes the release of 500 homes from the green belt, was recently found sound by a planning inspector.