Hybrid cars do not require an emissions test. The reason is that they cannot force the combustion engine to run during the test.
From the MoT tester's manual
8.2.1.2. Gaseous emissions
You must inspect vehicles with spark ignition engines first used on or after 1 August 1975.
You do not need to check:
L category vehicles
hybrid vehicles - with electric and combustion engines
hydrogen fuel cell vehicles
two-stroke engines - unless they are subject to a catalyst test
https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/8-nuisance