Eric, thankyou for all your detective work. I also found Thomas K. and Isabella Corran and thought them to be the most likely parents of Thomas jun. However, the census records for them don't appear to be applicable regarding the children.

William, son of Thomas jun. was my gr.gr. grandfather. As you say, he is not on the 1851 census for some reason, but he is on the others right up to 1881.

I must admit I hadn't thought of applying for Thomas and Elizabeth's daughter, Elizabeth's birth certificate which is what I'll do now.

Thanks for your help.

Jill