I don't recognize the type of boat, although it doesn't look WWII vintage.
The paddle steamer in the background looks old, but then, such boats seem to stay on forever in some parts of Britain, far longer than technological advantages would make you expect.
I tried to identify the time period by the flags
http://flagspot.net/flags/gb_roge6.html but it seems there's not enough difference between different royal flags to tell without a much better picture than is here.
It might help that there doesn't seem to be any sort of deck gun or anti-aircraft armament, but that could be just because it's just launched and would be added later, or because it was early enough that they hadn't yet realized the threat posed to ships by aircraft.
My suggestion would be to email the picture to the Royal Naval College at Greenwich, England and see if they can identify it for you. I've contacted them in the past about a model of an 1812 warship I was building and they proved to be quite helpful. It was even an American ship, but they still had information on a sister ship that told me a lot.
