I think you underestimate what children are taught in history lessons at
secondary school. A skill they learn is the interpretation of sources, and
so rather than learning grand narratives, they are taught to look for bias
and how to find a balance between different versions of the same events.
Open any school text book and the narrative paragraphs would probably take
up less than half of the page, with the rest dedicated to sources.
Plus the National Curriculum is not a compulsory list of indoctrination.
There isn't enough time to teach everything on it. Departments and teachers
choose the questions to concentrate on, such as "What can we learn about
Queen Elizabeth from her portraits?" and "Guy Fawkes: guilty or set up?". So
whatever the government is proposing about teaching with an emphasis on
Empire will, in actuality, probably be crammed into one lesson on a sunny
afternoon when Year 9s are more interested in who fancies who in their
class. Government declarations of this sort seem to be intended to be
crowd-pleaser more than anything else. Well, that's my opinion anyway!