Just ask them to fix it. I had an Octavia mkI owned from new that developed a strange noise and it was a similar engine mounted to the chassis but holding the gearbox. It had not been spotted in service or MOT but it kept having exhaust joint issues after downpipe / catalyst. I ended up diagnosing a knock on acceleration myself using a paintbrush handle pushed in - more vibration but knock disappeared. Mount was replaced that fixed the noise and exhaust had no further issues - clearly the excessive rotation of the engine block was causing this.

Make sure they fix it as there is a word of caution here - when the garage replaced it they said that many of these are fastened into captive nuts within the chassis and if the bolts are seized in and captive nuts break off(mine was ok) - Houston that's a BIG problem involving cutting/welding. I mention this as the securing bolts look different in the video? If they can't fix - reject the car.

Edited by Big John on 28/11/2022 at 21:46

MoT inspection manual....6.1.8 (a) ( i)............'severely damaged or deterioration resulting in excessive movement....'

You are in the hands of the examiner and their interpretation of 'excessive'. Sadly, their opinion almost always trumps yours, especially when the measurement is unquantified. However, I think that easily producing a noise of something banging against something else adds sufficient weight to your opinion that the movement is excessive enough to fail the MoT, and should not have passed. That should outweigh their opinion that it was OK. In view of the small timeframe, their counter argument that the deterioration might have occured since the test would carry very little weight. Hope this helps - good luck!