Just realised I should probably report this. Currently at work, so my apologies for not doing so in game.
I believe one of the dev team recently posted that users should get 2 character slots, with an extra slot given when you unlock klingons for a total of 3 slots?
I appear to be currently locked to 2 slots even though I have unlocked the klingons.
I think this is because I only had one character slot in use when I unlocked klingons. I have since created a second federation character and am now unable to create any further characters from either side as ive filled all my available slots.