My chi gave birth to 3 beautiful healthy pups at 12am this morning but for the last few hours she's been panting alot is this normal?  It is muggy in the uk at the min

Yes

If you are concerned about your dog you should be contacting your vet for advice as I'm sure you want the best for her.
Please let us know how she is.

Yes my girls frequently pant after giving birth sometimes for a day , they will also continue to dig after whelping . This is due a) to be tired after whelping and b) their uterus shrinking back  due to puppies feeding , commonly known as after pains . During whelping and for upto 24 hours after giving birth I offer my girls a good quality dairy ice cream which gives them energy . I also take them to the vets ASAP for a calcium injection which gives them a much needed boost .

Enjoy your puppies I hope all goes well. In my experience the first 3 weeks are critical. Any concerns contact your vet

I've bred Chi's for many years.  They pant an awful lot after birth from the uterus pain as it is contracting.

They don't handle pain well at all to be fair.

They do pant a lot but when this happened to me I went to the vet and he gave my chi an injection. Soon after she passed a black tarry looking substance but stopped panting and seemed less restless.