I noticed what I thought was a bit of play in the BB bearings on my HT11 chain set but when I looked closer the whole axle was moving side to side in the bearing cups. The non drive side crank appeared to be securely bolted to the axle and when I loosened the bolts I had to give the preload tool a few turns to take up the slack. Any ideas whats happening? It doesn’t seem to be a simple case of the crank being too loose on the splines.

It doesn’t seem to be a simple case of the crank being too loose on the splines.

Sounds exactly like that from your description, or have a missed something?

Spacers?

From experience, they need a good hard shove / tap when installing new to get the drive side in properly. then preload the non drive side& nip up the bolts.