The John Ashlin whose death was registered in St Pancras in Sep qtr 1858 was said to be aged 62, so born abt 1796 rather than c1807. His residence, according to the burial register at Victoria Park (nonconformist) cemetery, was 75 Harrison St, Gray’s Inn Lane. Burial was 25 July 1858.
Where was your John in 1851, how old, what birthplace was stated, and who was he with?