These two seem to vary by about £50. Is there much to chose between them otherwise?
Yes. The main differences are
1) The built in microphones in Edirol look like omni type and H4 are cardioids.
2) The Edirol has so called mic power for 1/8" input for external mics, while H4 has a true 48V phantom power and can accept professional XLR input mics.