You are writing this on an internet forum that is based in Canada.
We don't have MOT tests here. We have something like it, but it's not called that.
We don't have that bike model here in Canada. Therefore, for those TWO reasons, no one that you are talking to will have had that specific issue on that specific bike.
That adds up to, "you're talking to the wrong people".
Nevertheless, brakes are brakes, and the technical answers that you were supplied with are as helpful as can be expected under the circumstances.
You've either got air in the brake line, or seals somewhere in the brake system that are knackered (and there are only two places that have seals, the master cylinder, and the caliper), or the pistons inside the calipers themselves are munged up with dirt and brake pad dust so that the pistons are not going out and in properly.
That's it. Find the problem and fix it. There's an ocean between where we are, and where you are.