Hounslow council is reported to have had 5,151 children applying for entry to Year 7 in September with only 2,907 spaces available.
The shortfall of 2,224 places makes it the worst borough for shortage of secondary school places in England, according to a Freedom of Information (FOI) request obtained by education law firm Simpson Millar.
However, the council says the shortfall only affects applications made by parents from outside the borough.
The figures were revealed on the eve of the much anticipated secondary school allocation day (March 1) when parents and children find out whether they have been accepted into their preferred school of choice.
Simpson Millar say the findings reflect an ongoing issue, with appeals made by parents against their child's school allocation increasing by 10% between 2014 and 2015, and only one fifth of those appeals successful as parents don't understand the complex process.
'Get your argument straight'
Imogen Jolley, head of education law at Simpson Millar said: "We've carried out a further review and found staggeringly low appeal success rates in a number of districts including Portsmouth, Westminster, Newham and Kensington, while parents in the Isle of Wight, North Somerset and Barnsley enjoyed some of the country's highest success rates.
"This indicates something of a regional lottery when it comes to secondary school appeals."
The firm has urged parents to get their arguments straight if they are to have any chance of getting the school place they want, as most appeals fail because parents misunderstand what is required to be successful.
Although a child or family might meet the relevant social or medical criteria, appeals fail because parents misunderstand what is required to be successful.
Ms Jolley added: "Parents tend to launch appeals based on their child's academic strengths rather than focusing what is required under the School Admission Appeal Code.
"The Independent Appeal Panel is not concerned with which school is the best academically for your child, but whether missing out on their first choice will be of genuine detriment.
"A well evidenced case of harm to the social, emotional or medical needs of the child or a close family member, if the child does not attend that school, is likely to be successful."
Councillor Tom Bruce, Hounslow council’s cabinet member for education and children’s services, said: “Simpson and Millar’s statement has unfortunately resulted in headlines which may have alarmed parents and carers in Hounslow.
“To be clear, we received a total of 5,082 on time applications for 2,907 secondary school places.
"2,894 applications were for children from Hounslow and 2,188 were for children outside of the borough.
"We have therefore been able to offer every Hounslow child a secondary school place.
"Our priority is to ensure that every child from Hounslow is offered a school place which - given our growing population and the removal of local authorities’ freedom to build new schools – is no mean feat.
"Well done to all our schools and our admissions and place planning team.”