Hi Katt
I've been settling my little one into a creche too, my best advice is keep it regular, if you stop all the work done so far is wasted. When you do go make sure its a quiet session, I started to leave my little one in the afternoons when it was quieter, so he was brave enough to explore and have more attention from the adults. At first he was permanently on someones hip, now he is off on his own. Still cries when I leave him, but that is not uncommon and I know they stop almost 2 seconds after you're out of that door. Plus if the child was really distressed they would come and get you, always remember that.
I think the noise is the most unsettling factor, mine hate it apparently when others cry, also dont be late in picking up, they see other mummys coming and are always looking up for you!
I know just what you're going through and it is hard, and sometimes I'd be in the gym thinking non-stop about him, but if you stick to it, little and often, I'm sure he'll be fine.
PS: I agree with Bugsy, always pass them to someone, I never leave him on a mat, that does feel like abandonment to him (and me!)
Some creches you can wheel the buggy in and the children can sit securely in it and survey the surroundings and then get out when they feel confident. Do you take his comfort toy/blanket and favourite biscuit?