If possession of marijuana for personal use is tolerated in Amsterdam, and the  
UK is about to re-classify cannabis as a class-C drug with minor infractions  
not prosecuted, is it then possible to carry small amounts of marijuana for  
personal use back on a plane from Holland into the UK without fear of  
prosecution (assuming that no other countries/states are flown over en route)? 

Hi Jeremagne,

Interesting question.  Regardless if laws in the UK change, importing or 
exporting soft drugs (marijuana is classified as such) is an offense in 
Netherland:

“For the record, trafficking in (importing or exporting) selling producing 
possessing either hard or soft drugs are offences in the Netherlands. However, 
the use of drugs is not an offence.”

Netherlands Minister of Justice
FAQ: Have Drugs Been Legalized in the Netherlands
http://www.minjust.nl:8080/a_beleid/thema/drugs/qenaa.htm#a2.

The penalty for trafficking soft drugs is 2 years imprisonment and/or a fine of 
25,000 Guilders.

Netherlands Minister of Justice
FAQ: Drug Offense Penalties 
http://www.minjust.nl:8080/a_beleid/thema/drugs/qenab.htm#b8.

To prevent the export of drugs to other countries coffee houses in the 
Netherlands are curbing the maximum amount of soft drugs that a coffee house 
can sell patrons.  The amount was reduced from 30 grams to 5 grams. 

Netherlands Minister of Justice
What is the Netherlands doing to tackle drug tourism?
http://www.minjust.nl:8080/a_beleid/thema/drugs/qenab.htm#b6.

I’ve included an article from the BBC that might be of interest.

Keywords used:

ministry of justice Holland
amsterdam cannabis smuggle

Websites that may interest you:

Decriminalisation: Let's go Dutch?
http://news.bbc.co.uk
http://news.bbc.co.uk/hi/english/uk/newsid_693000/693257.stm

Regards,

Trailhead