Here is the GCHQ bit of RIPA, which makes reference to part of the bit you quoted.
http://www.legislation.gov.uk/ukpga/2000/23/section/42
GCHQs mission is to monitor all communications. Thus, to them anything will be proportionate. The over iew and scrutiny failed and failed hard - i have no idea why anyone thought it was acceptable to gather webcam data. (Maybe as a training exercise where the data is then deleted or a proof of concept?)