Are Plusnet able to tell if an FTTC service is suffering from contention perhaps between the cabinet and the exchange or between the exchange and Plusnet themselves?
These are the results from a BT Performance test. Sometimes the connection works OK and I would get a download speed of about 36Mbs:
Performance Test Results Report Basic Performance Test - Time Stamp Latency Download Upload Sunday 28 August 2022 | 12:41:40 30 Ms 4.17 Mbps 5.28 Mbps Advanced Performance Test - Download Test Download speed achieved during the test was 4.17 Mbps For your connection, the acceptable range of speeds is 20-38.67 Mbps Your DSL Connection Rate: 0 Mbps(DOWN-STREAM),0 Mbps(UP-STREAM) For your connection, the maximum achievable download speed is 38.67 Mbps IP Profile for your line is 38.67 Mbps Upload Test Upload speed achieved during the test was 5.28 Mbps For your connection, the maximum achievable upload speed is 10 Mbps IP Profile for your line is 10 Mbps Summary Advanced Performance Test - Result Message This test was not conclusive and further testing is required. This might be useful for your Broadband Service Provider to investigate the fault. Note:An error occurred while trying to retrieve additional details regarding your service. As a result we are unable to determine if the speed you received during the upstream test is acceptable for you service. Please re-run the test if you require this additional information. Please visit the Speed Test Guidance if you are unable to understand the test results.