Very simply you cannot receive remunerated instruction on a Private CAT aeroplane if it is group owned. The reason is that money changes hands within the group, this is permitted so long as no other money changes hands for the purpose of the flight. If the aircraft is owned by an individual or a husband and wife then remunerated instruction is possible. Unremunerated instruction on a Private CAT aeroplane is possible though unlikely unless you have an instructor in the group.
The IMC test or a Proficiency Check may be conducted in a group owned aircraft and paid for. See AIC 21/2000 (White 9)http://www.ais.org.uk/Uk_aip/pdf/aic/4W009.pdf
[This message has been edited by Noggin (edited 14 May 2001).]