Your booking reference number is the number you are required to enter on your passenger locator form before travelling to the UK. 

It is displayed on your PDF receipt sent at the time of booking one third of the way down the page.  Please keep it to hand as you will need it when registering your test and for your passenger locator form when you return.

The reference number is MAYFI followed by the number 0 and your 6 digit invoice number.