This would pose some interesting issues under the Data Protection Act which would require all airlines which operate into and out of British airfields to comply with the requirements of the Act. Firstly all of the fitted aircraft would have to clearly display notification of the fact that images are being taken, and what the intended purpose of taking the images is. A note may also have to be printed on the boarding pass. I am sure that someone more conversant in this law would be able to point out a number of other requirements on the airlines.
I also fail to see what benefit could be gained from cameras in the cabin. If there were an incident or air rage or some suchlike then there will be a sufficient number of eye witnesses to testify in court as is the case now. While CCTV images would cement the evidence, the cameras would not prevent someone who is determined to hijack a plane from doing so, it would merely record images of the act. I can't help thinking that this is a knee-jerk reaction that will not add a great deal to security.