Hi Andy,
Thank you, I wanted to go ahead and post what information I have found on Brocket so far. I as get new information I will add it to the forum.
In 1939 Brocket Hall was used by the City of London Maternity Hospital. During this time the 2nd Baron and Baroness Brocket lived at Kinnersley Castle and at there other estates (but I am not for sure). The hospital was run by the local county council. In 1946 the City of London Maternity Hospital took over financial responsibility from the county council. I am not sure when the Hospital closed and the hall was returned to Lord Brocket. I believe it had to before 1949.
The Imperial War Museum has a collection of 9 photographs taken at Brocket in 1942 for the Ministry of Information.
http://www.iwmcollections.org.uk/dbtw-wpd/exec/dbtwpcgi.exe The London Record office hold some records on the hospital. Administration: Reports concerning Brocket Hall Emergency Maternity Hospital H10/CLM/A/07 1939 - 1940
http://www.nationalarchives.gov.uk/a2a/records.aspx?cat=074-h10c&cid=6#6The National Archives site gives a little detail on the City of London Maternity Hospital and on there use of Brocket.
http://www.nationalarchives.gov.uk/a2a/records.aspx?cat=074-h10c&cid=0