I have learnt that it doesn't pay to speculate on what type and date a piece of pottery might be. But that doesn't stop me doing it!
In looking through the reference books I have to hand (I have listed them in the sidebar) this sherd seems closest to a Stamford ware crucible judging by the shape of the rim (from the A. J. Mainman book). There is a deposit on the outside of the sherd that could result from use in extreme heat. But this is wild speculation!
Although I show the sherd in cross section I do not think I have got its inclination right. It probably sloped inwards on the actual vessel.
I will not attempt to guess at this one but it does have a distinctive rim shape (like the top part of the Times Roman number "1"). I am hopeful that this, with the colour and type of fabric, will enable an expert to give it a date.
My first stop for dating will be the regional Portable Antiquities Scheme. This time instead of taking along a few pieces at a time I will take everything from the one dig and leave it for identification (if they will have it!).