To start with the info I have (from Volvo UK)
We are very sorry to hear of this. We can confirm that if you are not able to get your vehicle serviced or MOT'd due to COVID-19 we can confirm that your warranty on your vehicle will not be invalidated.
and
We can confirm that your Volvo assist will not expire if you get your vehicle serviced in the next 7 months.
Please add any details for other manufacturers