Thanks for all your comments.
I had to spend a load of vouchers before 31 May, so went into a sport shop for a helmet (for my two year old daughter when she's on the back of my bike). Surprise! Special offer on tents!
I got a three-man dome tent for 50 Euros. Took it to a friend's house a couple of weekends ago, and tried to put it up. A proverbial piece of urine, it was! Even with the help of a small child, it took less than ten minutes.
Dome, two carbon fibre segmented flexible poles, inner with groundsheet, outer with porch. All packs down to around 50cm × 20cm, though I reckon I could halve that using a compression sack.
Keith.