Brakes locking up unevenly

[Conrad]

When I do an emergency stop, one wheel tends to lock up way before the other.

It's mostly the offside front that locks up, but sometimes it's the nearside front, but not usually both together...

Does this suggest a caliper issue?

I've just fitted cross drilled discs and new pads all round (second hand anyway)

[kuSt]

u have ABS? if not i think you're supposed to use unvented disks.

[Martinaston]

Change the brake fluid and take care when bleeding it.

[Brianmoooore]

I've just fitted cross drilled discs and new pads all round (second hand anyway)

Sounds like they're not bedded in.
Second hand pads and discs are not good unless great care is taken that each pad goes back facing the same face of the same disc as it originally was.

[chief]

check simple things as well m8 like tyres (tread & pressure)
but my money will be on brians feedback (again!)