For just TSh, FT4 and FT3 I always use Medichecks Thyroid Monitoring fingerprick test. I buy when on offer. If you don't request doctor's comments it's usually back 24 hours after they receive your sample.
If it isn't on offer you might find MonitorMyHealth cheaper, it's an NHS lab in Exeter which does some tests for the public. The TSH, FT4 andFT3 test costs £29:
I've not used MonitorMyHealth so don't know how quickly the results are available.
Whichever service you use, do the test Monday-Wednesday and post the same day using a service which arrives next day if possible as you don't want the sample hanging around the lab over the weekend. Medichecks are currently including a Tracked24 envelope.
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