Thanks both for your advice. I checked with RBS but even though they also provide the One Account they don't offer the level of analysis that I get with One Account.
But... then I had an epiphany! I wasn't looking at this laterally enough and rather than worrying about what the online service can do, I'm now looking at a bank account that lets you download statements in a format that can be read by something like Accountz or MS Money (OFX files). See my other post re "Downloading statements from Nationwide".
Thanks,
Simon