Luggage storage in London

http://www.visitbritain.com/VB3-en-US/transport/gettingaround/usefultips/leftluggage.aspx - you have to give the luggage to a surly operator. So size shouldn't be a problem.

If, for whatever reasion you can't use the ones at Paddington, the service at http://www.tfl.gov.uk/vcs/ is generally highly regarded and operated by a different company to all the others. Tube to Victoria, follow the rail station then coach station signs, and turn right as you go in the main street entrance.

I kept my luggage at the Royal National Hotel in Russell Square. Only cost me a few quid. I was staying there immediately prior to having them look after it, but they never checked that I was guest, so I assume anyone can leave it there if they ask nicely.

Another vote for the Paddington thing.

There's luggage storage in one of the terminals (sorry I can't remember which one - not the international terminal, strangely, and I'm sure a quick Google search would turn it up). It's 5 pounds, flat fee, for 24 hours and is really very reliable and safe. I used it for a similar situation this past summer and was very pleased by how cheap and convenient it was. Plus, no lugging bags to & from Heathrow in order to store them - a huge bonus.

http://www.excess-baggage.com/contact.php#paddington. I've used the same facility at Kings Cross, and it's fine (if not a bargain). There can be queues at busy times, so arrive well in advance of your train to pick up your bags.

I did this exact thing this year with my friend. We arrived at Heathrow and had about 8 hours to kill before catching a flight out of Luton. We ditched our luggage at Paddington and wandered around for a while, but I have to warn you that the Left Luggage fee is a lot more than the old lockers were and you have to go through security checks to leave them there, meaning it's not open 24-hours.

Most London mainline stations have left luggage -- Holgate's link, though labeled Padington takes you to the list of locations of the company that seems to have the franchise. Also on the list are the terminals at Heathrow, so there's no need to drag your bags into London to a station. What isn't on their site, if I remember correctly from looking carefully last summer, is the price. At Kings Cross last August I think it was six pounds per bag per 24 hours (or part thereof). They x-ray the bags and ask you about any battery powered devices within.

I've used the http://www.excess-baggage.com/contact.php#paddington without hassle. They do x-ray your bags, and it wasn't cheap (about 6 quid a bag for a day), but it's perfect if you are leaving from heathrow: just across from the platforms.