No they most likely wouldn't know, but it does not mean that it is a good idea to do so. As others mentioned, it is, quite simply, not allowed to do so. And it is the sort of plan which sounds all innocuous until something goes wrong. All goes well and yes of course, people will be oblivious that you did something you couldn't but it just takes the one day when the lounge is evacuated due to some suspect bag somewhere, the one day when your train back to Heathrow is blocked and you miss your departure or can't spare the time to go to the CCR (and that one has happened to me before - stuck in a bloody tunnel - nothing that could be done for long, long minutes) or some other random issue which none of us will have thought about but which can disrupt plans.

Considering that apart from not being allowed, you would waste time needing to restore the ready to fly status (often not very long, but equally you cannot be sure as it depends whether someone is around that can fix it quickly or not), and that there are alternative options that work just as well (check the bag if it is big, after all in F, you have plenty of allowance, take it with you to CW if it is small, or leave it at the left luggage facility if it is big but you really don't want to check it), personally, I join the chorus of those who say they would really avoid this course.