A report from Research and Markets (extract at Business Wire) suggests that 28% of UK garden buildings companies are in financial danger. I haven't seen the full report so can't really comment, although the list of companies examined suggests that it's not specifically garden office specialists that are being looked at. It also claims that:
* five companies are blatantly selling at a loss to capture market share.
* average pre-tax profit was 4.6%
* average sales growth was -1.1%
From the correspondence I receive from garden office suppliers and from anecdotal evidence (including via this blog and The Shed magazine), my feeling is that the demand is high and growing.