Your stream says "HD." But sometimes it looks like HD. Sometimes it looks like a potato. That's bitrate fluctuation.
A British IPTV reseller whose bitrate jumps from 8 Mbps down to 2 Mbps and back up again is either congestion-shaped or using adaptive ladders poorly. Stable bitrate (within 20% variance) is the mark of proper provisioning.
Here's the technical view: many players show current bitrate in their stats overlay (TiviMate does this). Watch it for 10 minutes. If it stays between 6–10 Mbps, good. If it drops to 1–2 Mbps every minute, then spikes back up, the server is struggling to keep up.
In most cases, what actually works is ignoring the "HD" label and watching the bitrate number. A British IPTV service that delivers a consistent 5 Mbps will look better than one that fluctuates between 1 and 15 Mbps. Consistency beats peaks.
Scenario: you're watching a movie. It looks great for 30 seconds, then turns blocky for 10 seconds, then returns to great. The bitrate is seesawing because the server is overloaded. Your network is fine. The reseller's capacity is the problem.
I've seen an IPTV reseller UK with beautiful peak bitrates (15 Mbps) but terrible consistency. Every time a neighbour on the same server started a stream, your bitrate would crash. The server was oversold. The numbers looked good on paper. The experience was awful.
Honestly, during your trial, enable player stats. Watch the bitrate line. If it's a flat line (within reason), the British IPTV reseller UK has provisioned correctly. If it looks like a heart attack EKG, walk away.
A British IPTV reseller who delivers consistent bitrate is delivering consistent experience. That's the only kind worth paying for.