Mervyn,
Silver Tokens.
The Metpol. official website says that they were introduced in 1919. This is confirmed in the book "The Official Encyclopedia of Scotland Yard" (Fido & Skinner) who go on to say that they were issued to Commissioners, Assistant Commissioners and Deputy Assistant Commissioners. The text suggests (but does not definately say) that they are still issued. However, I know from information given to me personally by a DAC who was serving in that rank post 1993, that this is not the case. He did attempt on my behalf to discover when they ceased to be issued, without success. No one appears to know and Police Orders are silent.
Deputy Assistant Commissioner rank.
Again, the Metpol. website quotes 1919 as being the date the rank was introduced. The above quoted book suggests continual use to-date. However, the "Police & Constabulary Almanac" for 1956 makes no mention of the rank under the Metpol. entry for that year. So, your suggestion that the rank has had intermitent use seems correct.
Best wishes, Dave.