Some relevent advice gratefully needed please.

I am looking at doing a one way trip next week from LIS-MAD-LHR and as far as i can see i should be eligable to travel so long as i have a PCR test within 72 hours of travelling and pre- booking the 2 and 8 day PCR tests for the UK along with the Spanish "FCS health control form" and UK "public health passenger locator form".

Traveling for health reasons and i have dual UK and Portugal nationality.

Looking at booking on IB 3166 and checked on seat expert and it's showing as a A350, has anyone taken this flight recently and have any reports of passport queues at LHR.

Thanks in advance