Reversing Cameras' are usually mounted at high level, is there any sign of any previous fixing points, centrally, above or below the joint between the roof & rear panels ?
Guess you are looking for 3 patched/filled holes, 2 for mounting screws & 1 for wiring.
You could put the question on the Swift Talk forum. http://www.swift-talk.co.uk/forum/topics/contacting-swift-via-the-forum http://www.swift-talk.co.uk
It's monitored by a team of their employees & they should be able to give guidance, IF the Reversing Camera was an original fit.
BUT it could be anywhere if an "after market" fit.