I have a cat her name is sasha. She brings mice in to the conservatory, the dog gets jealous of it hence she swallows the mouse whole and alive is this normal I've always had dogs but never one what has done this. I no this is going to sound a bit silly but I can't get it out of my mind that the mouse is running around in her belly for a day or so anyway does anyone no of a way I can stop her and is it harmful to casey as its not every now and again this is nearly every day she gobbles it alive with one swallow and its down the hatch so to speak .

I don't know if it's harmful or not but I would tend to think it can't be all that good. If, in fact, the dog swallows the mouse without chewing or anything and that mouse really is live going down, it potentially could cause injury to the dog.

As far as the mouse running around inside the dog, stomach acid will take care of that and that mouse won't live that long.

Mice are carriers of intestinal parasites, namely coccidia and roundworms, you'll need to routinely have them checked (dog and cat alike) for these parasites and treat accordingly.
These parasites also live in the environment so it's a good idea to check anyway.
I can't picture that there isn't at least one chomp to kill the prey, I've never seen a dog eat a living thing that eagerly, but you never know.
As far as stopping it, I see a few options.
An exterminator
Keeping the dog out of the conservatory
Work on the "leave it" command.
Personally I think I would opt for trying to get rid of the mice, sounds like there may be many if it is a daily event. If you do, do it safely you don't want to risk your pets by keeping dangerous rodentacides around, call an exterminator and enlist their help or advice.
As far as mice running around in the stomach, a normal healthy stomach should empty in about 2 hours, and stomach acid is strong stuff.

Edit: After some research I just found this. I'm not trying to scare you but it may interest you to also know that mice have been known to carry salmonella, typhus, and leptospirosis.

http://www.macroevolution.net/diseases-carried-by-mice.html#.Uk4AK9K-qWk

My border collie catches mice very day, but thankfully he doesn't eat them. He leaves them for me, and I can tell you it isn't pretty. Most times you can't even tell it was a mouse. Okay, got to stop talking about this, it's making me sick.

I do agree with Lady Sam. I make sure that Rascal (our mouse killer) is checked regularly by his vet, and the vet is aware that he's a mouser. Frankly, I'm pretty darn proud of him, and encourage him to do this. We live right behind a field, and get a lot of mice in our home. The traps don't work nearly as well as Rascal does. :)