I've read the documentation a few times (or at least the parts that were relevant - lot of stuff that I'm not using).

The problem was not actually with REDIRECT, which works (apologies for misdiagnosing the problem) - the problem was that in the <Location> Apache2 configuration the actual location is followed by a Regexp, which altered the behaviour of the redirect.

Though this was meant to be the case in Apache 1.3 too (at least according to the docs), the behaviour was different - basically another location was picked up in Apache 2 that wasn't in Apache 1.3.