After I finally replaced the old HP Procurve 420 Access Point at the office with an Airport Extreme, HP came up with a solution to my problem. They decided to send me, free of charge, a brand new access point (since the 420 had been end-of-lifed).
This was very kind of them and now, sitting on my desk, I have a brand new HP Procurve MSM310 Access Point. It came with all the trimmings: two antennae, a power adapter and a serious steel wall mounting bracket. Compared to the Apple device it looks seriously industrial.
Weirdly, all four parts, the access point, the power adapter, the antennae and the wall bracket, came in four separate packages. The funniest of which was the one that just contained the two small antennae. Good business for DHL I suppose.
Now, I don't know if this device actually fixes the original Bonjour problem I was having, and I'm unlikely to find out. Despite the London address, HP sent a power adapter with a US plug.
Ah well, it's the thought that counts.