The 'sale by retail of alcohol', on an ongoing basis, always requires a licence. (The only exemptions from the licensing rules relate to trains, aircraft, etc, to Royal palaces, etc and also to certain 'temporary events' where it's simply necessary to notify the local licensing authority that the event will be taking place and that alcohol will be sold).
Actually, two separate licences are required. Firstly, there must be a premises licence, to show that it's legal to serve alcohol at that location. Secondly, at least one person must hold a personal licence and act as the designated premises supervisor.
Those rules cover both restaurants and shops.
This link goes to a commercial site but it provides a useful summary of the legislation. (Click the relevant links down the left):
http://www.licensingact2003.co.uk/home.htm
The actual legislation is here:
http://www.statutelaw.gov.uk/legResults.aspx?L egType=All+Legislation&title=licensing+act+200 3&searchEnacted=0&extentMatchOnly=0&confersPow er=0&blanketAmendment=0&TYPE=QS&NavFrom=0&acti veTextDocId=816417&PageNumber=1&SortAlpha=0
Your local council's website will probably have further information about obtaining the relevant licences.
Chris
(PS: Your post refers to two different types of licences. 'Off-sales' and 'restaurant' licences used to be separate but now all alcohol licensing, together with licensing for entertainment or late night food sales, has been brought under a common framework through the Licensing Act 2003)