The big problem with the flatpack shelving is length plus weight plus awkwardness, but weight on its own isn't horribly bad, about 11kg (25lb); if I can make it easier to carry, I can carry something else.
Step forward the oldest portable computer case I own. I use the term "portable computer" rather than laptop, since it is in fact IBM's blue rugged canvas(?) bag for the original IBM portable PC, which weighed about 30lb and was basically the original IBM AT with a slightly smaller keyboard and a built-in 6" (I think) mono CRT monitor. This case is STRONG - and so, luckily, is its shoulder strap. I just tried clipping it on to the strapping around the flatpack, and it's even balanced fairly well - I should have no trouble carrying that and say four extra shelves, some more feet for the units, and a couple of other small items.
VERY relieved - it's not a difficult journey, but it takes say an hour each way, didn't much fancy doing it twice more.
Then Thursday I will hopefully be able to get the old shelving cleared, move it out of the way (fortunately they're folding bookcases and easy to reduce in size), assemble the new stuff, and get the books back. Wish me luck!
And I would have got away with it if it hadn't been for those meddling... well, actually, entirely my own fault. I got off the bus on one side of the road and crossed over to Ikea; when I left I got on the same number bus going the other way, as I did yesterday, expecting to go back to the nearest station for the train back to central London.
What I hadn't realised was that the road was a spur off the main route - buses going in both directions come in on the other side of the road, stop outside a big Tesco there, then go down the road, turn around at a roundabout, and come back on the Ikea side and stop again. So the bus I got on turned out to be heading in the wrong direction, and I didn't know the area well enough to realise at first. By the time I'd sorted this out, got off, got on another bus, driven back past Ikea and on in the direction I wanted, I'd wasted at least 45 minutes, which meant I went home in heavy rush-hour commuting time and had to stand all the way on both trains. Not pleased, and the only person I can blame for it is me!