@samJCIf this is affecting multiple motorized heads (like the main cleanerhead and the mini motorized head) -  then this is an electrical issue with the main body. Please contact support for a replacement part.
And, while you mentioned that this isn’t affecting just one head. But if it were just one motorized head -  that head would either have a debris blockage or damage to its internal motor.

Please refer to this article for information - My Cordless vacuums brush bar isn't spinning, what can I do? | Dyson Community.

To contact Dyson please get in touch via one of our messaging channels, either WhatsApp or Facebook Messenger, where one of our team will be happy to discuss the next steps.  

To do this, simply click on our Dyson Support link, navigate to the ‘Contact us’ section of the page and select ‘Start a conversation’. 

Thank you Adam. It is affecting just the brush which I think needs to replacing but IT IS ABSOLUTELY IMPOSSIBLE TO MAKE ANY CONTACT WITH “SUPPORT”!! Believe me I have tried for most of the weekend.

Re-posting.

I spoke to Dyson using the live chat service over the weekend. I waited for no longer than 10 minutes. The frustrating part is they’ve buried the ‘Live Chat’ option in their automated assistant. 

If you use the return process flow, you’ll get an option to speak to an agent using live chat. 

G.