I am researching the posibility of importing goods from China to the UK (tyres).
a) How do you guarantee the quality(spec) of the tyres matches what
you ordered? I understand their are documentary letters of credit, but
they do not guarantee that the goods may be faulty/ out of spec etc?
b) Can the goods be send direct from our source in China to another
country with our own documentation and not that of the source of the
goods?

Re: Guarantee of quality:
 SGS (www.sgs.com) is one of the leaders in the field for quality
verification. One of the conditions listed on the L/C could be an SGS
inspection certificate prior to shipping.

As for part 2, shipping to different country directly from China, but
documents to issued by you:
I know this can be done. You need to discuss this with a banker
specializing in import/export.