Whether you are planning to travel to UK or from the UK make sure to find out which Covid-19 test you are required. You can make sure about these rules by contacting your Travel courier, Airlines or Train companies for examples, asking your travel agency or checking the UK government website on:
What do they check?
Depending on your destination, you may require to present one of the following;
Covid-19 Negative result (PCR Test)
Covid-19 Negative result (Lateral Flow/Antigen Test)
Proof of vaccination
Please note there is limited time duration between test and your flight to be qualified. For instance most countries accept negative test result within 72 hours of your flight while some other countries accept within 48 hours, 96 hours or different limitation.