Posted for "Gary Edwards" <gary21sn@hotmail.com>:
My take on the subject is that we are obligated to give ATC a full tail number until such time (which might not occur) the controller responds with a partial number, which in turn gives us an ok to then use partial numbers.

Any ATC's on the LML, please feel free to clarify my info.

Thanks,
Gary Edwards
LNC2 N21SN