Is a PCR test better than a rapid antigen test for travel?

We will be travelling to the UK at the end of the month, and I have been busy lining up all the various testing ducks needed to travel abroad and to return to Canada. One of the requirements that is receiving a lot of attention recently is for a molecular PCR test within 72 hours of returning.

The travel industry hates it, the mayors of border cities hate it, the USA hate it. Many are calling for it to be be changed to a less onerous and less expensive rapid antigen test. Even Canada's Chief Public Health Officer Teresa Tam says the current PCR policy is being "actively looked at".

I have always been of the opinion that the PCR test is a better, more accurate and more definitive test than the antigen test, and we should be going with the gold standard and not dumbing it down to the level of safety required by places like the USA and UK. After all, look how badly they are doing compared to Canada's COVID situation. But the more I think about it and look into it, the more I am coming round to the idea that maybe the antigen test is the way to go, at least for fully-vaccinated travellers.

Yes, antigen tests are less accurate (by some estimates about 20% false negatives can be expected, because the test is not as sensitive to low viral loads as PCR tests). But set against that is the fact that results are essentially immediate, so the testing can be much more timely. So, rather than an accurate PCR test three days before travel, a not-quite-so-accurate rapid antigen test on the actual day of travel may be more useful, and account for activities in the final few days of the trip.

That said, I think the test should be done before flying, and not two days later as in the UK, although an additional test two days after arriving would probably be wise too.

Let's see whether Canada's policy gets changed before we travel.