I'm having a problem with the front brakes on my kitcar (standard panda brakes). The car pulls to one side under braking. I have tried the usual things, stripped and cleaned the calipers, checked that neither is sticking, even fitted new pads, bled the brakes etc. The odd thing is that it doesnt always pull to the same side. The car recently passed an MOT and the brake tester showed an even braking force from both front brakes. Both front tyre pressures are even, and I replaced the front springs and shock absorbers last year (that didnt help either). Anyone got any ideas?

A bit too much tow-out, perhaps? Check the tracking, and tyre wear:
excess wear on inside edges of both front tyres.
Under those circumstances the tyres are pulling a bit in opposite directions, the one with most grip takes you that way.

Possibly worn tie bar bushes causing excess tow-out under heavy braking.
At rest the tracking may well check out OK.

Or dubious alignment, or rigidity, in the suspension of your kit car??

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Also consider instability due to excessive rear braking (locking up) caused by an inappropriate load balancing valve (the kit car is probably a lot lighter at the back than a Panda, if you've used a Panda valve block), or even no valve at all.

The tiebar bushes look pretty worn and they have small spilts in them so I'll try replacing them and then have the tracking checked. The chassis is made from really thick box section and the plate the suspension mounts to is thicker than the same steel area in the panda so I'm hoping its not that flexing.

There isnt a load balancing valve for the rear brakes, but the car does start pulling long before the brakes lock up.