Louise Evans from business advisors Grant Thornton says promotion could be worth up to £150m for the club and will have knock-on benefits for the city and Wales.
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Wales's largest teaching union welcomed today's results, but says the drop in entries for non-core subjects is still a concern.
The number of pupils achieving A*- C grades has remained at 66.6% for the third year running. The overall pass rate was 98.7%.
Prostate cancer kills over 540 men in Wales every year and more than 2,500 are diagnosed annually.