This thread has proved to be very enlightening so thank you all for your help. It seems that ...
William Baker is the son of Lammas Lane and Mary Baker née Owen.
Mary married Thomas Baker in Dudley in 1825 but he died in 1837 and was buried in Old Swinford.
I can't find any record of her marrying Lammas but they are together in the 1841 census in Coseley st. Bilston. Their son Lammas was born in 1840 and died in October 1841 but they went on to have four more children as listed earlier in this thread.
I cannot find any evidence to explain why any/some of them reverted to the "Baker" surname but the best explanation I can come up with is that Lammas and Mary never married and this would have proved difficult for official transactions. It could also explain why their marriage cannot be traced?
Lammas isn't "James" in the 1851 census but it could be easily mistaken for that.
Lammas also appears as Lambas, Lamas, Laimbus and that's before the transcription errors creep in. He was a hairdresser for most of his adult life and died in Netherton in 1885. George Henry Baker was one of the executors of his estate.
I sent an "e-bay" PN to the owner of the indenture but have yet to receive a reply.
Many, many thanks to you all.