The same thing has already happened in Cardiff.
Cardiff numbers use the (029) area code and initially the local numbers began 20xx xxxx only.
That didn't stop many people assuming the area code was 02920 or 0292.
When the 20xx xxxx numbers had all gone, new numbers were issued all beginning 21xx xxxx.
That didn't stop the local press incorrectly moaning about a new 02921 code:
http://www.walesonline.co.uk/news/wales ... -26546062/Now that the 21xx xxxx numbers have run out, new numbers in Cardiff begin 22xx xxxx.
All of these come under the single 029 area code.