Okay I understand, thanks for confirming the shape.
So the cups would be considered "demitasse" in size and this set would originally have been marketed as a coffee service.
The number "13403" refers to Shelley's general pattern name of "Duchess" with the blue celeste ground.
The "Duchess" pattern is one of the many so-called "Elegant" patterns (those produced in three colors) that Shelley manufactured during the Second World War and through the 1940s and early 1950s.
As part of the war effort, the Staffordshire potteries in England were required to cease all manufacture of decorative china during this time, except for export and so almost all of this production ended up in the dollar markets of Canada, USA and the Antipodes.
Each piece is beautifully decorated with much "heightening" of the enamels by hand-painting (over a color print of the design), and of course all the gold enamel is applied by hand.
As for value, there is still a reasonable quantity of Shelley Duchess (pattern # 13403) about, even though it's getting on a bit (most of it dates to the 1950s & 1960s) which is a good thing as it means there's enough to sustain a buoyant secondary market (auctions & on line sales) for collectors building sets and/or seeking replacements.
So here are the value ranges (in AUS$) to expect if you were to sell at your local antique auction house or on line (eBay/Etsy/Gumtree etc)
6 cups & saucers........................50 - 80 (for all)
creamer.................................... 20 - 30
sugar bowl.................................20 - 30
Total ......................circa AUS$90 - $140
The full retail or 'replacement' value is AUS$280 and is what you should insure the set for.
As far as selling is concerned, the easiest option is at your nearest or best antique auction house. The only factor to take into consideration is an auction house's not inconsiderable seller's commission of roughly 20% -a sliding scale depending on the hammer price; each auction house has its own rate and scale.
You may net a little more on eBay/TradeMe/Gumtree etc (fees are about 10%), and you may get a little more if you were to sell the cups individually, say, but there is packing and shipping in such a way as to ensure safe arrival, which is time consuming.
Selling to a local consignment store or antique dealer is also a route worth considering. Dealers usually agree to pay the low end of the auction estimates if they're interested. I would contact your nearest antiques mall and ask who the local Shelley, or English china collector is. They will know and give you contact details.
This is probably the easiest way to go, because it requires little travel and no shipping worries.
I do hope this helps!
Please let me know if you would like further assistance with this, I would be glad to.