Love these old adverts. One of the nicest things about them is that there's not an aberrant apostrophe to be seen. (Ignore me; it's just one of my bêtes noires).
Whatever was "An Ordinary" that you could have at the New Brighton Hotel on Sundays during the summer?
Only just saw this post today and I wondered the same thing. According to dictionary.com:
14. British (in a restaurant or inn), a complete meal in which all courses are included at one fixed price, as opposed to à la carte service. 15. a restaurant, public house, or dining room serving all guests and customers the same standard meal or fare.