New Royal Cypher

 Today saw the release of the new Royal Cypher for King Charles III

There will be a transitional period of a few years as it's introduced on coins, bank notes, stamps etc.  

British Police Forces will no doubt have there own timetable for changing their helmet plates where they do still use the generic E II R Royal Cypher. I expect the London Metropolitan Police will probably take the lead and be the first to replace theirs with the new design. They may choose a phased approach by issuing initially to new recruits, once the new badge becomes available.

The London Metropolitan Police has always used the Royal Cypher on their helmet plates. Others, such as Avon & Somerset Constabulary have adopted their own design for their helmet plates since 1990. 

Hertfordshire Constabulary helmet plates have a separate ER cypher centre which can be removed and replaced with the new CR design. The helmet below was made by Hobsons in 2009.

Hertfordshire Constabulary Helmet 2009

Surprisingly, the Channel Islands Police on Guernsey have continued using a helmet plate which uses a King's crown from the reign on King George VI. 

Island of Guernsey Police Helmet - current