Would anyone know from where I can buy the daimler sovereign owners manual please ? Thanks for your help

 

Paul you are about to send me your E mail address with regard to the heater switch. When you do I can send you a PDF file of the 420 service manual if that's what you want. You can buy original hard copies off E bay and they start from around £28. The service manual tells you how to take it apart.
https://www.ebay.co.uk/itm/134030665...Bk9SR9zr7snwYA

The Jaguar 420 owners manual is a different thing and describes what all the buttons in a 420 are for and some service requirements. These are a lot more expensive at around £176 off Ebay.
https://www.ebay.co.uk/itm/233987526...Bk9SR-rn-cnwYA

 

https://blackwells.co.uk/bookshop/pr.../9781855201712
For a new, printed copy of the service book, I'd use Blackwell's website above. For secondhand, there's eBay as Cass has indicated. There's also Abebooks. For the latter, the supplier will be a bookshop and generally the condition is good.

The operating handbook looks hard to find and very expensive.