On closer reading, the BBC article says:
"The government has committed £17m"
"The Department for Education's £17.34m, which will be spread over four years...."
"The Department for Education said the money came from a portion of the schools capital budget dedicated to "policy priorities" such as free schools and academies."
It sounds like the Government will give £17m to support a pet project, but won't give £50m to fund primary places across the borough.
Lambeth & the Government going head to head over what they will & won't fund rather than Lambeth having confused priorities.
The Government will also be funding Katharine Birbalsingh's Free School - I suppose that's another "policy priority" - and I wonder if that will be at the expense of the other State secondaries in the borough, some of which were sink schools under the last Tory Govt but are now outstanding schools...