Probably more hassle than it's worth. Where would I get the drums from?
The pots are about £3 each and should last a decade or two, so worth it.
Lowes wants me to register as a trade customer before showing what they stock.
Scots Plants Direct looks the best bet I've found so far: http://www.scotplantsdirect.co.uk/growing-needs/pots-containers-baskets-and-more/plastic-plant-pots-big/heavy-duty-plant-pots-25-litre.html
Thankfully my slave moles are busily making mole hill potting compost for me to fill them with.