Here is a link to the application form submitted http://www.ukplanning.com/ukp/doc/Application%20Form-5749329.pdf?extension=.pdf&id=5749329&location=VOLUME5&contentType=application/pdf&pageCount=11
It shows 1905 sq. metres of proposed institutional use (I believe this is the museum) and refers to proposed opening times for the museum. The parts of the mansion proposed to be demolished date from the 1950’s.