I accessed a copy of the 1968 official full death certificate and the occupation of this Alexander John Thompson is stated as retired 'Statistical Officer' at the 'General Register Office' which was his occupation according to the LOCOMAT article referenced. So this confirms the death details as follows.
June 17th 1968 at 36 Link Lane, Wallington, (in county of Surrey at time of death, now in London Borough of Sutton).
A note on the source as requested.
In the UK to obtain a death certificate copy (or birth, marriage) an application with payment of £9.25 has to be made to the UK General Register Office (GRO) online or local register office.
Ancestry sites like www.findmypast.co.uk with a paid for small credit give the registry index details and these details are used to order.
Because of the cost(!) it’s a service I only use very occasionally but does potentially provide a firm answer to a query that the ancestry sites may not unambiguously resolve.
I can send a certificate scan via email for personal use to anyone if interested which has more info’.
I think the sort of citation for a formal reference would be:
Alexander John Thompson, certified copy of death certificate (age at death 83), General Register Office, UK. Entry – Sutton, Surrey, 1968, Apr-Jun, vol. 05E, p.192.