Every day is now identical in the UK, unlike in most other European countries. Therefore, the motivation for this request is not religious (I am an athiest) but a recognition that society in this country could benefit from a day of rest in some areas of its activities; 24 hour or specifically, late licensing is one of these.
Due to 24 hour licencing laws, it is now commonplace for those who live in towns and cities to be woken up at 3 or 4 am every morning by drunk people coming home from pubs and clubs. For many (though I appreciate, not all), Sunday night/Monday morning marks the transition between the end of the weekend and the beginning of the working week. It does not benefit the economy of this country to have people turning up on the first day of work hungover from their own activities or tired, through disturbed sleep, from the activities of others.
I do not disagree with late licensing in principle and appreciate that nighclubs and pubs need to make profits in these challenging times. However, I believe that asking for restrictions on Sundays is a reasonable compromise that in effect, amounts to a request for a reinstatement of previous restrictions.