UK clinical trials can't compare drugs against patented alternatives

A comment explaining US law on this:

http://pipeline.corante.com/archives/2013/02/26/standard_of_...

Why would the fact that a drug is patented prevent it from being used in clinical trials ? Can't a patented product generally be used as the buyer wishes once it is purchased (subject to other laws of course) ?

The Wikipedia article on the First Sale Doctrine, which applies to copyrights and trademarks led me to the Exhaustion doctrine for patents, which isn't so clear cut it would appear: http://en.wikipedia.org/wiki/Exhaustion_doctrine

Before bringing a new drug to market, companies have to conduct clinical and field trials which usually requires testing it against others already in the market. Under the current system, carrying out assessments using patented drugs is an infringement which can incur big costs.

...He added: “The main thing is to boost competition. Under the patent laws, clinical trials have been shifting off-shore - so this is part of our agenda of attracting more clinical trials here.”