I went abroad last month and did it properly, paying for a day 2 PCR test in advance, and putting the serial number on the passenger locator form. I also did the test (well, actually, my wife did it for me...)
Other people I know bought the click-bait cheapo tests for £1 that require you to drive to the middle of nowhere in the middle of the night to do the test just to prove that they had booked a test. Then of course, they did not do the test, and heard nothing from either the testing company nor any government agency.
I'm going away again in a few weeks to Stockholm (to pay homage!) and want to know If I can also get away with this. It could save £40 for me and the missus, and I get the satisfaction of not playing along.
Were my friends just lucky?
To avoid climate change you should avoid traveling. But if you need to travel, which frankly it sounds like you do not, then you should pay for the test. That's what law abiding citizens do.
Pretty easy to avoid.
The PLF only looks for a test code thats a recognised format - it doesn't verify the test is assigned to you or even if its been used before.
For example Randox use RANDX1234567 (1234567 can be any 7 digit number).
Then you just need to knock up a fake email in notepad saying you've ordered that test with the same number (plenty of examples online).
In your case i'd use the same number as your previous test and just change the dates on the order confirmation email.
There's literally no further checking at all.