The thing is I would rather not go through each attachment one by one if possible since this creates an unneeded complexity. An overarching copyright statement would achieve to circumvent this. I cannot find a single reason why we should not seek this.
Also "unless otherwise stated" is a very problematic statement as the website itself provides that statement to all documents and attachments without a copyright notice. Hence why contacting MPs can be an easy way out for everyone.
BBC and commercial providers can be compelled on the basis of public interest since the recordings are briefings of the people compiling the reports. These document a record of the progress on the report over time. It also provides witness accounts etc. They compliment the report well.