Parents will find out on Friday whether their long and hard- fought battle to stop the planned expansion of a primary school has been successful.

Bristol City Council's cabinet councillor for children, Peter Hammond, is due to decide by the end of the month whether to go ahead with proposals to increase the size of Sefton Park infant and junior schools to take 630 pupils.

The £6.9-million scheme has been fiercely resisted by some parents, who say the site is too cramped for that many children and who also object to the possible demolition of a historic building on the site in Ashley Down Road.

The opponents concede that more primary school places are desperately needed in Bishopston – a fact that has been proved by the revelation earlier this month that dozens of families in the area have not got places for their children in any of their three nearest schools.

Both the Sefton Park parents and their protest group Agro (Ashley Grange Residents Organisation), and the new group of parents who have not been allocated schools, known as B PAC (Bristol Primary Admissions Crisis), want to see the council revert to a previous plan to build a 210-place primary school a short distance from Sefton Park on the City of Bristol College's Ashley Down campus. This proposal, backed by the Liberal Democrats when they were running the council, was reversed by Labour in January last year.

Many of the parents believe the U-turn was prompted by the intervention of Gloucestershire County Cricket Club, which was concerned that having a school on the college site – known as the Brunel field – would threaten its ability to stage big matches.

But the council said the reason for the change was that it no longer favoured building single-form entry schools and would prefer to put the 210 extra places into Sefton Park.

It has since consulted parents and residents on three possible options for the site and has carried out a feasibility study. Opponents have put scores of questions and statements to council meetings outlining their concerns about the plans.

Mr Hammond and the two top council officers involved, Annie Hudson and Kate Campion, met residents on Tuesday and Mr Hammond will meet the school's governors on Wednesday before making a final decision. On Monday, he revealed the council was considering putting a third reception class at Sefton Park for 2009, as it did in 2008, to help meet some of the shortfall of places in the area.

Bristol West Lib Dem MP Stephen Williams raised the issue in Parliament on Tuesday, saying the shortage of places would put particular pressure on the Ashley, Bishopston, Henleaze and Redland wards.

He told the House of Commons: "If we win control of the council at the elections in June then we will be pushing ahead with plans for a new school."

Lib Dem councillor for Bishopston Bev Knott confirmed that this would be a priority for the party.

"It has become more and more clear that the new school is the best way to meet the shortfall rather than trying to cram more children on to an unsuitable site," he said.

The Lib Dems are now calling for a special meeting of the council's children's services scrutiny commission before mid-March to examine the problem and the emergency plans to cope with it.

Councillor Clare Campion-Smith said: "The uncertainly about schooling for some of our very young children is causing real distress to families.

"The Labour administration appears to have fallen asleep at the wheel in not anticipating and acting on the problem. These children are not pawns to be moved around the board. They need a place in a local school."