Hi can anyone give me some advice please?

Since last week my car seems to have lost power, and cuts out when i try to accelerate.
I took my car to my local dealer, and they hooked it up to all of their computers and machines, but couldnt find any fault codes.
Since then they phoned up Vauxhall HQ, and they said it MIGHT be the gasket that is gone. So they have ordered that part and it wont be here and fitted to my car till thursday/friday.
My car is still under warrenty, so it will be replaced free of charge.
I had my car serviced from the dealer last week too, as i thought that, it was due, and it should solve the problem.
It didnt and the garage just gave me my car back, and said bring it back on Thursday.

The thing is that my car is undriveable, i just managed to get it home, which is 2 mins away. The car was gonna cut out so many times, and there was such a lag for it to pick up any kind of speed. It is quite dangerous for the people who are driivng behind me for example when i am leaving roundabouts, and other people jump on with speed and my car is taking for ever to accelerate....

Anyhows my question is that since it is going to take a few days for my car to get fixed and its undrivable should i get a courtesy car?
If i did, would i have to pay anything for it? As the my car is still under warrenty? What about insurance etc?
I dont have a clue as i have never had a courtesy car before and this is the first major problem ive had with my car.
Its just that i really need my (a) car to drive. and its going to be a few days till mines is fixed.

Also i would ring up Vauxhall HQ themselves to get some proper info, but i cant find any numbers to call.

Any advice would be appreciated.