Under these circumstances you have several options. The first one is to begin work and give the requisite notice required to the local authority. This is not advisable unless one has taken legal advice and it is a certainty that your construction will definitely comply with existing Building Regulations.
Another option is to resubmit one’s full enhanced plans to the local authority and await their approval.
A third option is to appeal against the decision.
The final option you believe a local authority’s decision to be incorrect is to refer it to the Secretary of State for their determination.