Thanks Crab, I think something like what you describe was happening.
When I introduced cyclic first before collective it obviously flared the disc with low angles of attack on the blades but low disc loading giving rise to the shuddering and loss of lift.
By introducing some collective first loaded the disc a bit more allowing the severe flare of the disc to take place without causing any problems.
It was sort of like the entire disc was stalling rather than the blades singularly.