There is no real reason why you should get questioned. Of course if you show up with dreadlocks and wearing hemp clothing, all bets are off.
There is nothing unsual in your plans and in fact I am doing something similar from Canada next week. The possibility of being questioned as to why I am flying into the UK, then out, then back to the UK, then back to Canada, has never even crossed my radar. It is a normal visit to Europe itinerary for many people.