There was growing evidence today that some kind of hypersonic jet may have been the cause of the mysterious bangs heard over both the UK and the US on Saturday. 

Engineering expert Dr Bhupendra Khandelwa told MailOnline he believes the loud, repetitive bangs sounded like an experimental jet engine called a pulse detonation engine (PDE).

Other theories - including weather phenomenon or meteors and space junk 'burning up' in the atmosphere - have been largely dismissed by experts. 

And a video showing a PDE being tested in a lab appears to add weight to Dr Khandelwa's claim.

'It makes the same kind of pulsing sound as the one on this audio,' he told MailOnline after listening to a recording of the bangs that was taken in south London on Saturday night.

'When we run a test engine it's a real industrial noise and you can hear it for miles. We have people coming to us asking to make less noise or keep it to the daytime.'