PCR test for travel

Does anyone know how you get the PCR certificate that you're fit for travel? I've tried searching but all I've found are self test home kits but that either won't provide me with a certificate or the results are sent out after the 48 hour time frame.
Or can I do it through my GP with the doctor signature?
I'm travelling to china this summer and they require a hard copy certificate that my PCR test is negative.

The thing to note with Covid requirements is that they keep changing.

The UK Government's information at https://www.gov.uk/foreign-travel-advice/china/entry-requirements (currently) makes no mention of a PCR test being required -- it says this:

"From 29 April 2023, China has changed its COVID-19 entry requirements for all travellers entering the country. You must undertake a lateral flow/rapid antigen test 48 hours before boarding your flight. You must declare your negative test result by filling in the Health Declaration Form via the China Customs website, or through the China Customs App or WeChat account. Airline officials will no longer check test results. However, upon arrival in China your test result may be checked by officials at customs."

A previous version of that page did mention PCR tests: "From 8 January 2023, China has changed its COVID-19 entry requirements for all travellers entering the country. You will need a negative PCR test within 48 hours of the arrival of your flight in China."

As @Surnia notes, you can't use NHS tests for the purposes of foreign travel.

Thank you! I've had a look at the declaration form and it seems simple to fill out, a bit too simple as it just asks whether you're positive or negative without asking for proof of any test. Am I right to assume that I can buy a normal lateral test and take a photo of the test in case they ask for it, after submitting negative on the form of course?

Does anyone know how you get the PCR certificate that you're fit for travel? I've tried searching but all I've found are self test home kits but that either won't provide me with a certificate or the results are sent out after the 48 hour time frame.
Or can I do it through my GP with the doctor signature?
I'm travelling to china this summer and they require a hard copy certificate that my PCR test is negative.