You simply need to appoint a shipping (clearance) agent to handle the paperwork for you. Many of the airlines themselves will undertake this too. It is not recommended that you try to go through the clearance process yourself. What you should be concerned with is that copies of the bill of lading (or airway bill in the case of air freight) is sent to you or your agent by your supplier ahead of the arrival of the goods in the UK.
There's more on this that might be helpful to you at:
http://www.figurewizard.com/article....d_the_Far_East
Joe.