What is the difference between High Street and Designer?

I have been giving some thought today, in light of London Fashion week and Angie's New York blogs, to the difference between high street and designer.

Is it price? The high street now offers a high and low end alternative, at the low end of the market you have Primark selling jeans for £5.00, whilst at the high end Whistles or Reiss command prices upwards of £150.00 for a dress. In turn the Designers are producing more affordable diffusion lines such as Armani Exchange or McQ.

Is it quality? High price does not necessarily guarantee high quality and sometimes surprisingly good quality may be found on a budget.

Is it Fashion Week? UK high street retailer Topshop now showcases Topshop Unique at London Fashion Week.

Where do boutiques and boutique brands fit into the mix?

I'm therefore interested in your opinion of what constitutes designer and why? and do you have a mix of designer and high street in your wardrobe?

Thank you for your time