Thanks to everyone for their responses. I am happy that this is probably what caused the "weirdness". Having never experienced ABS before, I didn't realise it would be so violent.
At least in future now I know that if it happens to just keep the pressure on the pedal and everything will be fine.
Tom
100000% ABS.
In the dry/Wet if its cutting in then you are breaking like hell for something, keep your foot fully pressed and as you said it'll stop .... however in the snow, at low speed, you'd probably better taking foot off and pressing it slightly more gently, keeping your foot pressed just leads to a solid pedal and very little stopping (as you experienced).
ABS in dry/wet - great
ABS in snow at low speed - bloody scary.
take foot off and try again.