We have a very long and detailed thread here about scanners in the UK. I suggest that you read at least the last few pages.

There are many ways to avoid the very few scanners at LHR. Often transfer passengers and fast track passengers will never even pass near one as not every checkpoint has them.

Add to that the rate of scanning is extremely low when compared to the US, and is secondary only, and is a MMW at LHR. The machine frankly is not in use very often (I fly through/from LHR almost weekly now, various terminals except T4) In the example you gave, you would have absolutely not have been scanned as there are no scanners in those locations.

Your chances are extremely low of even being selected, and they seem to avoid those who are obviously unable to use the scanner. My experiences for myself and others with physical issues have been good to very good to excellent at LHR.

I really don't think that this will be an issue.