Thanks Derek.
i have had a quick look at the Cockayne memorandum and the author Andries Cockayne has written, (at page 206)
'Francis Cokayne, probably the eldest son of George Cockayne and his wife Elizabeth Angell, resided at Chaddesden and died there in October 1658
I did wonder myself if Andries had jumped a generation so Francis may have been the father of Caleb. Clearly though we need to find a birth record for Caleb which may assist us. I know Andries states a date of birth of 1650 for Caleb, I do not know though where this was sourced from
Regards
Eric