Ironstone China - Ashworth

Good afternoon all.
When I purchased this serving plate/dish, I thought Ironstone China was the name of the maker. However, having now looked a little deeper I can see that Ironstone is actually a combination of clay and china stone...and has been made since the early 1800's.
My well used plate/dish has a clear mark stating Ironstone China but I am unable to identify/date it further. Can somebody please help me with this?
Thank you.

Are those letters just above the word Patent?
Can't quite make them out.

Charles Meakin also made ironstone and used a similar crest.
No "England" would mean pre 1891.

I've had a closer look at the letters above the word 'Patent'. I'm not sure they are STD as the first looks a little like an X! I'll try and take a better pic a little later and add it o this thread.
Thank you for all your inputs.

I've tried my best to enhance this image of the crest/mark: I can see that Naomi may be correct and it may read STD...though its not very clear.
The Meakin suggesting is interesting: though the name 'Meakin' does not appear, there is a single 'M' mark nearer the centre of the base. Did Meakin sometimes just use a letter rather than their full name?
Thanks for all the help.
Jack.

The exact Ashworth mark is shown here: http://www.thepotteries.org/mark/a/ashworth.html

That's brilliant janetpjohn, thank you.
It looks like my plate is made by Ashworth between 1862 - 1891, so quite an early piece.
Thanks to all who helped pinpoint this.