Is there anyway to download a customised version of twitter boostrap (where you can edit the colours, grid widths etc) that gives you the css in .less format?
Bootstrap is in Less: https://github.com/twbs/bootstrap/tree/master/less (as of 3.0.0)
There is a SASS version here: https://github.com/jlong/sass-twitter-bootstrap
Edit: You can "fork" one of those versions, & add your own edits to it. You can use GitHub for free if you do not mind if your fork is available to others publicly.