Silly me, just checked their web page, and they do indeed have an academic test, that must have come in to force fairly recently? I don't recall that happening in the past?
The WGSG website has a link to their admissions which confirms:
"Applicants under criterion 7 will be required to take a verbal reasoning test and mathematics test, which will be used to assess their academic abilities. No minimum score will be required to gain admission, places being offered strictly in descending order of applicantâ€™s standardised test scores. Preparation for the tests is unnecessary. The tests will be administered by the school jointly with, Bushey Meads School, Parmiterâ€™s School, Queensâ€™ School, Rickmansworth School, Watford Grammar School for Boys and St Clement Danes School. Applicants to more than one school under criteria requiring a proven measure of academic ability will be assessed by these jointly administered tests."
So Clement Danes should be doing the same test. Best check directly with the school.