Thank you for your posts.
Samuel being a half brother of William is something that I have considered, but not being able to find any marriage for the father Samuel has not helped.
Thanks for the Norfolk Record Office item - I had missed that. The Sarah Minns mentioned is Samuel's niece, a daughter of his brother William Riches. It is now on my list for my next (not very soon) visit to Norwich. Presumably the 1873 declaration about Samuel's name would have been made by Sarah Minns, Samuel having died in 1855.
Samuel's will is below in case it helps:
Will of Samuel BLAKE of the Tally Ho Public House, Kentish Town, St Pancras, dated 8 Apr 1855
to my nephew Samuel RICHES £1000; to Ellen HYDE my housekeeper £100 and bed and bed articles? in her bedroom; residue to be equally divided between my brother William RICHES of Thurton, Norfolk and my nephews William RICHES, Jeremiah RICHES, and my nieces Sarah MINNS and Hepzibah OXBOROUGH; I wish to be buried in Thurton, Norfolk and I wish my nephew Samuel RICHES and Vincent HOWARD to be executors;
Signed Samuel BLAKE his mark
Witnesses: Vincent HOWARD, Samuel RICHES, William RICHES, Ellen HYDE;
Appeared personally Vincent HOWARD of 40 ....? Street, Marylebone, Middlesex, Gentleman, who made oath that he is one of the witnesses to the will of Samuel BLAKE late of the Tally Ho, Winchester Place, Kentish Town, Middlesex, licensed victualler, that the said Samuel BLAKE made his mark on the will and that the above witnesses were present Dated 11 Apr 1855
Proved 26 April 1855 to executors Samuel RICHES the nephew and Vincent HOWARD PCC