The Hunter Telephone collection have Monarchs in Australia .

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Looks like they were called the Plessey CdSS 

In 1976 the Abbeyfield Road Digital Technology Centre was opened in Lenton to enable the development of digital switching technologies. 

Initially, the PDX was developed and manufactured there. In the early 80's the iDX was designed and successfully launched into the newly liberated telecom market brought about by the privatisation of BT The iDX was the first of a long line of digital switching systems which are still being developed and sold today (2021)  as the Realitis range. 

COSS/Monarch (small to medium size) and DKS (Keysystem) were other very successful digital systems developed in this period. Telephone manufacture continued to be a major part of the site activities including novelty phones such as the Mickey Mouse model. 

Extract from http://www.samhallas.co.uk/repository/documents/siemens_100.pdf 

I wonder how many UXD5's you can get for £million in 1989 ?

http://www.plesseyattheedge.co.uk/assets/images/galleries/downloads/GPT_Link_Aug_1989.pdf

link to pdf