Defender 90 - uneven braking

I would appreciate some help in which direction to go on my 300 TDi CSW braking system. Firstly on this vehicle all the calipers, discs and pads were replaced together about 1200 miles ago - but the clue maybe that a year has gone by in which to do those miles and things may have partially siezed due to lack of movement. The braking until recently has been excellent but a week or so ago I started to get an intermittent longish brake pedal and at other times a normal pedal - whatever the condition, it never felt like an air in the system problem - always a solid pedal with good braking but at times a longish pedal.

So I replaced the brake master cylinder as there were signs of seal wear (small black bits in the reservoir) and have bled the system twice. The new master cylinder has made a difference in as much that the pedal is more solid than ever but I still get on occasion a longish pedal action. I've noticed also that under heavy braking the vehicle pulls to the nearside.

Can I ask if this could be due to sticking caliper pistons which look okay (no rust or mud deposits) but when observed with someone slowly pressing the brake pedal, do not move exactly together at the same time? I will be bleeding again as one of the pipe unions had a very small weep when the new master cylinder was fitted - this now fixed but it could possibly have drawn in air (but I don't really think so).

My first thought was pistons or caliper not sliding .. I'd suggest a piston and seal kit to fix it, fairly easy job ... well it was on my Disco ..

Wheel bearing? Causing pad knock off?

I had a similar problem and it turned out to be a wheel bearing like jacksta has said.

Just a quick thank you for the responses - it is a front wheel bearing failure, in fact it looks like it's totally disintegrated. I've only done a partial strip down so the hub is still fitted at this moment but many of the rollers have turned ninety degrees and I'm really surprised it still rotates.

I've ordered a 52mm socket as I don't like undoing nuts with chisels etc so I'm looking forward to seeing how bad it really is.

Thanks again