Test broadband for streaming in the UK
Ofcom can show predicted broadband availability by postcode. For streaming, test the line and room you already use as well. The two checks answer different questions.

Look up the property first
Enter your postcode and select the property where you will watch. Note whether the quoted speed is predicted and which connection type it refers to. If you rent a flat, check which line is actually installed before comparing packages.
Try an evening test on the same TV
Run the first test near your TV, then repeat while the rest of the household uses the connection normally. If you can use Ethernet on your device, test the same programme on a cable before changing a player or plan.
Separate Wi-Fi from programme availability
An improvement on Ethernet is a reason to investigate the wireless link. A single programme that fails everywhere needs a different check. Write down its name, the time and the exact app so the support team can see what you tested.