hey Thanks for ur reply!!
I ended up getting a second opinion as the vet I went to said if mel didn't pee by herself within 24 hours she thought we should put her to sleep - we went to another vet and luckily we did- it turned out that on a new X-ray she Realised it wasn't clear - she ended up opening mel up and she had SEPTIC peritonitis which would have killed her quickly-- she took about a LITRE of infected fluid out of her near her bowel and put her on extremely strong anibiotics..,
within 24 hours mel peed herself... She has gone from strength to strength since then and although she will be on antibiotics for the next 4 weeks..
She was allowed home for the weekend and had another scan on Monday to see if there is any more infection building up and thank GOD there wasn't! She is eating weeing and pooing herself now. She had her tail removed yesterday so she is coming home today

The moral of the story is : IF U HAVE ANY DOUBT AT ALL, GET A SECOND OPINION FROM ANOTHER VET- if I didn't follow my intuition, mel would not be here now and would have been put to sleep last week. Thanks for ur help and advice Guys xx