I've been trawling through all the regs around LPG. I've had a look through PD 5482-2005 part 3 (via Manchester online library) and it doesn't specify a wall thickness in that document. However, the BS EN ISO 10239 document does state a minimum wall thickness. The 2008 versions of this standard required a wall thickness of 0.8mm but the document was revised in 2014 and now states that a 0.6mm thickness is acceptable (up to an OD of 12mm). AFAIK this means that standard 10mm microbore from screwfix is acceptable.
This point has come up on canalworld before now, but google searches seem to return the older posts stating that we must use the thicker imperial copper to comply with the standards. Please correct me if i'm wrong.