You have two options:

1/ Change the Wi-Fi name/SSID and password on your new router back to the settings on your old router. Or;

2/ Connect each of you One’s to your router with an ethernet cable and change the wi-fi settings within the Sonos App.

Whoa. Wiring just the satellites is not a great idea.

I suspect the new router SSID somehow didn’t propagate to the Ones. Although they’ll attach to the Arc’s own signal in use, when they boot they may need the router SSID temporarily.

I would wire the Arc temporarily then boot the surrounds. If that doesn’t work, factory reset the surrounds and re-add them.

Ok thanks for the swift response. I connected the left speaker to the router via Ethernet. I disabled WiFi, but now the app doesn’t recognise the left speaker. When I try an reconnect it to the system it says it is not connected to WiFi. Perhaps I just simply do a factory reset on each Sonos one. Have you a link for that?

Do not disable “WiFi” on any of your Sonos units. It will only lead to trouble. Re-enable it.

If it’s not convenient to wire the Arc temporarily than reset the Ones and re-add them as surrounds. See https://support.sonos.com/s/article/1096 and https://support.sonos.com/s/article/2927

Ok when I returned the left Sonos one to the living room it is now recognised in the system  but still no WiFi connection or sound 

Hi ratty. Ok I went through the factory reset and reconnected the 2 S1’s as surrounds. But there is still no sound and the white line is solid

“White line is solid”? Could you explain? 

Hi ratty, I went through the whole process again and it has worked this time. Thank you for your help. Re the white line, the indicator on the arc is 4 dots, the indicator light on the ones is solid. I mistakenly thought they should be dots as well. 
thanks for your help