Flying Stockholm to London on Scandinavian flight, then 16 hr layover in London Heathrow, and then London Heathrow to Washington Dulles on United, and then Washington Dulles to DFW on United.

All one ticket bought ticket on United.

Do I need to retrieve my bag in London? I would prefer not to, so if I do need to retrieve bag, and plan to visit Central London what are my options?

Thanks.