12 hour layover in London. Where to store luggage? In mid-March I'm going to have a 12 hour layover in Heathrow. I figure this is plenty of time for me to pop into London, see some sights, check out a museum, eat some food, and be back at the airport in time for my flight. But I have one question: Where can I store my luggage? 

I don't want to walk around London all day rolling my big suitcase with me, so there has to be a place for me to store it in the airport. On the Heathrow website it looks like there are storage lockers inside the terminals, but my Virgin Atlantic flight will land in terminal 3, and my Lufthansa flight will take off out of terminal 2.

I'm not sure how to handle this situation. Are there luggage storage lockers at Paddington Station? Should I just bring my bags with me to Paddington and store them there?

Thanks for any help, guys.