Labour and Liberal Democrats MPs have vowed to fight any move to allow new grammar schools to be created.
Senior figures from both parties reacted to reports PM Theresa May may be considering lifting the existing ban in England to boost "social mobility", calling it a backwards step.
The Sunday Telegraph said a new wave of selective schools could be announced as soon as the Tory conference in October.
The education secretary has previously said she is "open minded" on the issue.
Grammar schools are state secondaries that select their…