In reply to captain paranoia:
Even the gov uk website admits it's a ripoff
"You cannot use an NHS test for your PCR test. You must use a private test provider.
You will need to enter your COVID-19 test booking reference number on your passenger locator form.
If you’re in England for less than 2 days, you still need to book and pay for a day 2 COVID-19 test. You must quarantine until you receive a negative day 2 COVID-19 PCR test, or until you leave England, whichever is sooner."