To take a protest to the skies would in theory be possible.
It would require a basic knowledge of avaition, two cynlinders of compressed helium gas, rougly 100 large size latex balloons (available on internet) and a harnass (climbing harnass would suit). It would be important to use strong rope and it would be essential to seek assistance with people who had knowledge of physics, aviation etc..


DISCLAIMER: I am not encouraging any individual to undertake such a task, merely illustrating that such a procedure would be possible. Flying within London without the permission of the Authorities is illegal and is not encouraged.