For handbuilt, I’d go Ultegra hubs, or Hope if you can afford them. CRC have 105 5501 hubs on sale at £45 a pair if you’re really strapped for cash. DT Swiss R1.1 rims are pretty light and have double eyelets for strength. Open Pros are also great. Make sure you get decent double butted stainless spokes (DT Competition or better), and get them built by someone who knows what they’re doing. Look for a DT Swiss/Madison/ATG trained mechanic.
For factory built, Aksiums are a good start, as are Shimano RS20s. Bontrager Race Lites are great looking, light and pretty strong for only £250.
As crazy-legs said, most roadie wheels are fine for cross, so take your pick.