In reply to woolsack:
As others have said, the short answer is no. A £5000 bike isn't ten times as fast as a £500 one. That said, road bikes can roughly be broken down into the following price segments:
£500-£1000 Basic road bikes, with aluminium frames and entry-level wheels and components, starting with Shimano Sora or equivalent, upper end with Tiagra and 105.
£1000-£1500 Entry/mid level bikes. Above the cycle-to-work cutoff, you start getting high-end aluminium frames with 105 or Ultegra and carbon frames are starting to appear, albeit with entry level components and wheels.
£1500-£2500 Mid level bikes. Entry level Carbon frames with 105 or occasionally Ultegra level components, still with basic wheels.
£2500-£3000 Mid/Upper level bikes. Mid level carbon bikes with Ultegra components. Very much in the middle of everything, but often with lower spec wheels.
£3000-£4000 Same as above, but with better wheels. Electronic shifting is starting to appear at the upper end.
£4000-5000 Race bikes. Mid-Upper level carbon frames with electronic shifting of top level mechanical groupsets such as Dura-Ace or Sram RED.
£5000+ What the pros ride.