@Luke_Stern
I'm not quite clear whether you're meaning one 6 year period or various short periods adding up to 6 years. Maybe a couple of things worth thinking about are that firstly you'd likely be aiming to highlight productive, interesting activities you managed to do during the time 'off' and, secondly, that you'll certainly need some pretty good corroborative references to show you were doing what you say you were doing and in the place(s) you were doing them. I'd think that second point is pretty vital when it comes to security.
Considering the economic conditions over the last few years it can't be uncommon or unexpected for applicants to have periods of unemployment (I had a few months of unemployment after university, most of my classmates did, although having claimed jobseekers it did allow it to be corroborated). A solid 6 year gap does of course sound more difficult to shed in a positive light than an accumulated period of 6 years over a longer time frame, but there's a lot more to a CV than just job experience, as long as you can provide context for the gaps.
All you can really do is put in the application and try and highlight the positive aspects. The fact that you started a business and it didn't fold within the first 12 months is a pretty obvious one, most others seem to!
Best of luck.
