The most up to date advice can be found on the governments DVSA website, there is currently an extension for 6 months for affected vehicles, but you must ensure that your vehicle is safe to drive.  If your car was registered between 23 March 2017 and 30 June 2017 please refer to Finance and Warranty section below for additional important information.
https://www.gov.uk/guidance/coronavirus-covid-19-mots-for-cars-vans-and-motorcycles-due-from-30-march-2020
Advice for Northern Ireland, Channel Islands and Isle of Man may be different, please consult the relevant authority.