"We have been told there is no money available until possibly the year after next. Our staff and pupils are working in intolerable conditions and this can't go on," said Michael Nesbitt, the headteacher.
Parents at Manningtree are currently being balloted on opting out and the result is expected around July 11. Its head and governors are not concerned at the prospect of a Labour government and the party's intention to abolish GMstatus. If it opted out, the school would not object to LEA representatives on the governing body as long as the parents and members of the community made up the majority.
Manningtree is one of five or six in the country holding opt-out ballots. But the number of schools investigating the GM route has slowed to a trickle. Since April three secondaries and seven primaries have voted in favour of going it alone; three secondaries and five primaries against, according to Local Schools Information.
Staff at Manningtree were balloted on opting out before the governors' resolution and voted six to one in favour of the move.
The practicalities of working in overcrowded conditions are beginning to take their toll on teachers, according to Mr Nesbitt. The school has three permanent, but poorly-equipped science laboratories and two makeshift ones. The music department buildings are subject to six-monthly health and safety checks.
"We have a fairly mature and stable staff here so they have become used to the conditions. But not surprisingly, they are increasingly telling me they need more space."
If the school leaves local authority control, Essex will be a step nearer to handing over complete responsibility for ensuring there are sufficient secondary school places to the Funding Agency for Schools. At present this is shared between Essex and the FAS.
Chris Pearson, a member of the education committee and county councillor for Manningtree ward, said the FAS would take over the authority's secondary school planning functions if a further two or three opted out.
He denied that there was a need for additional accommodation at Manningtree. "If there was a problem the authority would have a statutory responsibility to provide it. There is no guarantee the FAS will do so either, so the governors' claim that opting out will lead to capital grants has no foundation."
Martin Rogers of LSI said it was unlikely opting out would undergo a renaissance in the light of Labour's moderate new education policies. "There is nothing in Labour's paper that would trigger an acceleration in opting out, because they have not created a safe haven for these schools," he added.