Hello Dizzy - welcome to the thread, - Smee has described exactly what will happen at the clinic - there's nothing I can add to that, except that in some hospitals you may have to wait for another appointment to get your results, - some are same day results - it's just luck of the draw.
There can often be quite a lot of waiting around at the breast clinic, so arm yourself with a good book or your ipod, and change for the coffee machine.
If possible I would recommend taking someone with you for moral support - I always found that helped.
As jchoc says - there's a very good chance it is nothing sinister, - they always tend to err on the side of caution with breast lumps, but it is much more likely not to be cancer. Good luck with your appointment - and stick around if you want a bit of hand holding while you wait 
jchoc - really sorry about your Dh's nan, - how sad
Bless her - 99 is a great age, I bet she had some interesting stories to tell before she became ill.
amber - yay for your friend, great news, sorry you are having a rather hectic time atm though, sit down at once, and have a

AtoZ - as the others have said a few days won't make any difference in your treatment, but obviously that's not the point and I can totally understand why you are so angry and upset. It is shit when they mess you about - as if cancer treatment wasn't stressful enough, especially when you have to be an inpatient and have got yourself all psyched up and ready. I really hope they sort it out asap.
Smee - I have had trouble getting halloumi, - can't remember where I last bought it, I think it was sainsbo's, - I know Lidl don't ever have it. I have got a nice recipe somewhere for grilled marinated Halloumi, which I can let you have if you want it.
Just to completely lower the culinary tone, - it is 'end of the month desperately search in the freezer' time chez Kurri, - so we had Toad in the Hole made with Linda MacCartney cocktail sausages (which I don't actually like very much, but DH had a phase of buying sausages every time he went to the supermarket, - we also have about six hundred Quorn frankfurters which are akin to toxic waste IMO) 