For the records for the City of London Cemetery in Manor Park, the Corporation website appear to be only offering a research service of the early registers. I certainly have searched the register online for a relative but a link doesn't seem to be on the website anymore. Here is a link anyway - https://www.cityoflondon.gov.uk/burialRegisters/ - it is images only, there is no index. You should be able to 'visit' your relative still but even if there was a gravestone, it may have been removed with newer graves above. Regards June