Orkney Image Library

As a landlubber I'm sticking my neck well out here, but that's the coronet shared by both the Royal Navy and British Merchant Navy cap-badges (though mechant navy shipping companies weren't obliged to use it). So I would guess this piece of porcelain was produced for the Royal Navy, but by whom I haven't discovered. I dare say more than one company produced ceramics to RN specifications.

That's the 'naval crown' as used by the Royal Navy ... look here:
www.royalnavy.mod.uk/training-and-people/the-rn-today/ship-s-badges-and-flags/ship-s-badges/the-naval-crown/index.htm

used as backstamp on a piece of a HMS's porcelain

thanks for the info , the crown was on the inside and the makers mark on the bottom was an anchor but the name was on the bit of the plate I didn't get !

The anchor mark originally belonged to Chelsea manufacturers but was often copied in later times. For the time in question I would suggest to search after Longton (Industrial porcelain factory Anchor Porcelain C°. Ltd.), Longport and their mother company Davenport. As far as I know all of them worked for the Navy at some times.

there is a snippet of writing left which would match your theory , thanks