Absolutely not true in all authorities. All food premises are inspected initially, and high risk premises are visited far more often than those classed as low risk. For example, a pub serving just packaged crisps would likely be visited once every couple of years, while a higher risk premises such as a sushi restaurant would be visited every six months, depending on their last score. If, for example, a kebab shop is inspected and comes up very poor, if it's not shut down immediately, then it will be inspected soon after on a date agreed with the owner, and an improvement will be demanded.
Each premises is scored on a hazard and compliance basis, as set by the FSA (http://www.food.gov.uk), and the final scores will go some way to determine when the next visit is scheduled. Now that a score is published on the Internet, these rogue restaurants know they need to pull their socks up or they'll lose business.
HTH