My Cat Had Her 1st Kitten At About 7am This Morning But Has Not Had Any More And It Is Now 12.10pm. Should I Be Worried. She's Purring And Is Feeding The 1st One.

If you're sure there are more kittens to come, then I'd start to be a little concerned.  You might want to call your vet (or ER since it's Sunday) and ask how long you should wait before helping things along.  There's a condition called uterine inertia, where for one reason or another, the uterus stops contracting... If that's the case, she'll need meds to jump start the process again.