I dont know the right answer, as I know people who have done the same, and another that wasnt.

Coming from Oz, I was advised by my travel agent (my sister), to purchase a return ticket, as I was only entering the country on a VISIT visa. (my hubby was already in Dubai)

Both times, arriving here on a return ticket, I have used the "london" leg of the flight, and cashed in the return part of the ticket to Oz.

You may be alright,...Im sorry I cant give you a "correct" answer, I was told, as its a VISIT visa, then that is what you are doing...visiting, then leaving..