Pulling to left under braking

You got a leak at all? Spongy pedal?

Could be a few things..

Don't necessarily assume that it would be only a front brake issue. You didn't mention whether you've checked both ends.

Tyre pressures OK?

I'd expect one or more sticky caliper pistons. Start by removing the pads a caliper at a time, insert a substitute wooden spacer (About 10mm thick initially. You're safe down to about 3mm in the later stages once you've got piston movement under control.) to prevent the pistons being forced out all the way. Stroke the pistons in and out. Force them out with the brake hydraulics and back with a lever taking care not to damage the pistons. You'll probably need to do this several times gaining a little more movement on each occasion, hopefully. Take care not to allow the piston to c*ck in the bore. Clean the piston as much as possible (string wrapped round the piston can work well) every time before forcing it back into the caliper. Remember that the outside diameter of the piston is the surface on which the piston seal slides. Some brake fluid as lubricant can help. You need to use common sense on how you do this: I can't cover all potential problems.

If you can get all pistons moving freely you've probably solved your problem. (Note that if you need to replace the pads with new, the piston will have to retract fully.) Don't be too surprised if a piston won't move at all! You may have to sacrifice the piston (it'll be scrap anyway) and use sliding joint pliers to extract it.

If you can't free all the pistons it's not too difficult to fit new pistons where required and seals. It's a caliper off job to do this comfortably. It's probably not a good idea to do just one caliper on any axle.

Pedal is ok but can be spongy on first press, then firms up ok. The brakes don't always pull but maybe 7/10 times so thinking sticking caliper. It is used off-road most of the time so gets well caked in crud.

Andy

Mine does this every year, though not strongly. Invariably it's been the rear brake pistons (either) getting crudded up and deciding not to play ball anymore. Quick piston/caliper overhaul and it's OK for another 10-12 months .. I really probably ought to get new calipers ....

Even new calipers are not a guaranteed long term cure. Unless you use the vehicle in such a way as to make the rear brakes do some of the work they will inevitably deteriorate with time through lack of use.

I found that on my Defender. The improvement in stopping power was quite significant

Check wheel bearings - if they are failing, this will allow the hub and disc assembly to move laterally as well as rotating! If the bearings are different on the two sides, this will show up as a pull.

Happened on my Disco years ago when I was in Zimbabwe. Front left bearing had worm prematurely and was about to collapse.

Regards Graham Carter