Ben Bradshaw MP introduced a new regulations under the Clean Neighbourhoods Act which enables any council to introduce new dog control bylaws.
More info here.
http://www.thekennelclub.org.uk/item/295/
Each council in England and Wales can take parts of the act and make their own policies. Some have been introducing the new laws more vigourously than others, and they are enforcable and punishable in the first instance by a fixed penalty. Then if you do not pay, you are likely to be prosecuted by the council.
The Kennel Club have set up a group called KC Dog which is working towards keeping the new laws realistic. Dogs should be able to excercise off the lead to keep them healthy. You should find more information on there about the whole thing. They also keep you informed if your council is planning any changes as some have been guilty of changing the law, not advertising or signposting it and sending out dog wardens to generate revenue.
For example in Exeter, you have to have a dog on a lead everywhere. Some councils are more lenient and use their common sense and keep it to certain areas like graveyards, childrens recreational areas etc