Front wheels locking up at low speed in wet?

Like it says in the title - one of either front wheels are locking up and skidding at low speeds (>20mph) under braking on wetish roads. K reg 200Tdi 110. Anyone got any ideas? I know that the front wheels are meant to lock up before the rear, but this is getting stupid. Tyres are General Grabbers with decent tread.
Could the rear drums be worn? Would this have this effect?

Vulch

No idea about defender's. But in my old metro I had air in the system and it kept skidding a wheel when it shouldn't have. At <20.

Has it always done it or is it only recent?
Normally wheels locking is down to poor grip. I last suffered it in my old S3 which ran on Xplys but that was over 25-years ago, since changing to radials I have never lost grip on the road. Are the Grabbers open tread, old & hard etc?

Check your front calipers slide ok and not seized or sticking, check the pistons also move back and out without problems.

Discs you can check runout with a DTI gauge see if not warped and pads not glazed.

Worth a brake bleed for the price of a litre of fluid and do check rear brakes as precaution anyway.

if it int ya brakes. Ya front bearing is starting to seize up.

Thanks everyone! Good stuff. The tyres are probably pretty old and hard - not much wear as I'm too old to drive it like I stole it - but probably getting on a bit. No cracks yet, but that could be the issue - thoughts?

I put on new discs and pads about 18 months ago and all seems fine - I had a look a few months ago and all looked OK. There has been a low squeal under braking sometimes - could that be the shoes on the back?
I will bleed it through too.

Cheers,

Vulch

My guess would be either the bearing or a dodgy calliper