Ok, thanks everyone - have remembered a few more things he did 'wrong' like only fitted the main wallplate/hanging bracket - not the second one which slots in lower down the main plate - he also decided to drill new holes in the horseshoe thing which connects flue to boiler and screw them into top of boiler - rather than asking me to go and buy the appropriate screw to fit it through the proper hole. Also he did not fit the clip things to the valves (not sure how important they are). I thinkm sum total is phone CORGI tomorrow - let them know everything he has done and let them decide.
I checked his CORGI number and it corresponds to the name he gave me - advertises under and to the address on his emails... his assistant who ran the gas pipe probably wasn't a CORGI though - and I guess he should have been? or maybe a trainee is allowed to do that?
this is ok so long as the qualified engineer is on site and supervises the install to ensure it meets the gsiur