Leadership at St John Fisher says £5m is needed to bring the school into line with others in the Harrogate district.
The new headteacher at the school, Rob Pritchard, told the Harrogate Advertiser that he has plans for John Fisher that will add 17 new classrooms and refurbish the entire school at a cost of £5m.
Mr Pritchard, with the support of the school governors, said he has permission from the diocese to pursue a stream of funding called the priority schools building programme (PSBP), but to do that he needs the support of North Yorkshire County Council (NYCC).
He said: “It is a great old building but what we need is extra capacity in terms of classrooms because the school has grown over the last 10 or 15 years and for whatever reason extra classrooms have not been added.
“That is why we need to plug into this fund for the school to be able to grow, and it isn’t an awful lot of money - we are only asking for £5m.
“A brand new, state of the art school is £50m, and the £5m we’re asking for will make the school sustainable for years.
“I think other schools have had a more recent influx of capital expenditure, though I have no evidence of that, just what I have seen as I’ve walked round them.
“And the building here is not something our parents are massively concerned about, but I am not going to come and do nothing here.”
However, as John Fisher is a voluntary-aided school the funding available is different to what academies like the Grammar School and Rossett can access.
The Harrogate Advertiser has also learned that the deadline for PSBP has passed and no more applications will be accepted for five years.
NYCC strategic planning manager Suzanne Firth said: “John Fisher is essentially too late to apply for PSBP. Voluntary aided schools can apply via the local authority but we did a piece of work ourselves to see which projects we were going to apply for and John Fisher was not one of them.
“PSBP is about the condition of buildings, not whether they are big enough or fit to deliver the curriculum, so John Fisher did not emerge as one of the higher priorities.
“We also look at the priorities that have come forward from all of the diocese, so John Fisher will be competing with other schools for a slice of that cake, and it is not a big cake - it was short of £1.8m in the last block of funding we had and the other block we get is not for voluntary-aided schools.
“It is good the head has aspirations, but the current situation is quite limited in terms of what can be achieved.”