Thanks for the tips and the recommendations. It looks like Cyclus is the clear favourite for a headset press. Although I expect I'd be fine using a rod-and-washers press, the collective wisdom of YACF says a proper press makes the job easier. I've had no problems removing headset cups and installing crown races using spare tubing.
Do you know of a UK retailer of Cyclus? (My Google fu turns up RoseBikes in Germany, but I'd need to order a few items from Rose to make the shopping costs worthwhile.)