The Tories have denied their education policy is in "disarray" after a second frontbencher defended grammar schools.
Mr Grieve said new grammars should be built if needed
Dominic Grieve told his local paper that if more grammars were needed in Buckinghamshire, they should be built.
One shadow minister has already quit after leader David Cameron said it was "delusional" to expect new grammars.
But the party denied Labour claims its policy was in "chaos" saying Mr Cameron had only been referring to areas that did not already have grammar schools.
In an article for the Buckinghamshire Examiner, Mr Grieve - shadow attorney general and MP for Beaconsfield - said he was "pleased" the Conservatives were looking at ways of reforming the comprehensive school system nationally.
But he added: "There is no question of our changing the selective education system in Buckinghamshire against the wishes of the local community.
"We must also ensure that if further grammar or secondary schools are needed they can be supplied within the county."
There are 164 grammar schools in England - choosing pupils by academic ability at the age of 11 - with 10 local education authorities considered to be fully selective.
David Cameron has faced a grassroots rebellion over his decision to ditch the Tories' traditional support for grammar schools and academic selection.
He said the party had not built a single new grammar school during its 18 years in power, that evidence suggested they did not enhance social mobility and called it "delusional" to think they would be able to build more in the future.
Instead, he pledged support for existing grammar schools, but backed an expansion of Labour's academies programme instead.
On Tuesday Europe spokesman Graham Brady resigned after being reprimanded and warned to stick to his brief after saying selective schools could boost overall educational standards.
The policy was also denounced by members of the Conservatives' influential 1922 committee of backbench MPs as "ridiculous" and "absurd".
Europe Minister Mr Brady has already quit over the row
On Thursday, Labour's chief whip Jacqui Smith said: "Dominic Grieve's comments have thrown the Tories' schools policy into further chaos.
"At the same time as David Cameron and George Osborne pledge that new grammar schools would not be built, their own shadow attorney general says that allowance should be made for new grammar schools to be built.
"The Tories are in complete disarray."
But the Conservatives say Mr Grieve's comments do not contradict party policy.
Shadow Education Secretary David Willetts said: "David has said absolutely nothing that is out of line with Conservative Party policy.
"I do understand that in parts of the country where they've got grammar schools, as demography changes, so they will come forward with how their grammar school system needs to change."
Mr Willetts said Mr Grieve's argument had been made in the full knowledge of his discussions with Buckinghamshire MPs and councillors - and he did not rule out building more grammar schools in such areas if they were needed.
"I am fully aware that in a place with rapid demographic change, like Buckinghamshire, you are inevitably going to face questions about whether you need to build more schools or not," he added.