Trish - I was terrified of having a bike and even now I'm a bit scared - especially doing right turns on Holloway Road and going through the lights at Angel. I'm lucky that most of my route can be done down quiet back streets - going through Clerkenwell and Smithfield in the morning is a joy. Have you tried looking at the cycle routes on TFL? They often suggest the backroads and canal paths that might help you avoid the bad bits. Are you along the Bakerloo? I think that can be a bit hairy because most routes go along Edgware Road - but you'd be surprised how considerate most drivers are. As long as you cycle defensively and politely you tend to get treated with respect.
Another thing I used to do was 'get lost' on the way home from work. I would spend 30 mins to an hour walking down streets I never normally used until I bumped into a different tube station. Or you could walk down to the Thames and along the Thames path to Westminster or Embankment. There are lots of things you can do to mix it up a bit.