Originally Posted by
HH6702
Could always be
G-ALCY
G-BLCY
G-CLCY
G-DLCY
ALSO
I think most airline systems use the last two or three letters to identify a particular aircraft, which is why they tend to use -LCYx or LCxx, rather than xLCY. G-ALCY and G-BLCY would both appear as "CY" in some systems. It is a hangover from early computer systems used in the industry. I don't think the CAA considers -xLCY a block of registrations either, so it might be more complicated/expensive to do.
I imagine -LCXx or LDNx might be the next series used, they both appear to be unused. Another option might be G-CFEx. G-CFEC would be a good one!