100 miles a week, assuming I do my 12.5 mile each way commute 4 days a week on average. I miss some weeks with holidays but some holidays and weekends involve leisure cycling. I've done just under 5000 miles in just under a year, confirming that average.
People I know at work who cycle mostly have shorter journeys than me, with a few being similar. I don't know any significantly longer ones. However people heading North or South from Central London, rather than West like me, would have a much hillier journey.