I have just swapped my front wheel hub for my spare and since doing this I heard the abs kick in buy only every so often and only light breaking around 5mph, all other speeds noting happens.

The abs sensor is an old used one and not the one I took off. But even so would it not do it at all speeds?

Check that the abs sensor is clean, and that none of the holes in the sensor ring are covered in any dirt or grease.

Will check that today, are the rings more sensitive to errors the slower they go?

yes, as the slower the wheel rotation, the longer it see's the blocked ring, which the sensor interprets as a locked wheel.

Well ended up working my day off so will have a look at cleaning it Saturday.

My front left brake is not working, noticed that the brake is still rusted up, was working before working on it, so curious wgat has stopped it working. At least I know why it is kicking in abs

Caliper fluid line blocked or still collapsed at flexible, or caliper partially seized on sliders?. Did you disconnect fluid lines at all when changing the hub over?.

We didnt disconnect brake so assume will just have to look, will look for the above thanks for your suggestions

Took disk off and checked today, brake calliper cleaned and re greased and piston clean. Only thing left is sensor so will try that. Would an intermittent or faulty sensor show on vagcom

it will only show as a fault if the ABS ECU is getting signals way outside its range, if the ABS is behaving oddly but not triggering the ABS light then the car still believes nothing is wrong as it is still receiving data (albeit wrong data) from the ABS sensor.

Right, ill pop and get a new sensor and see then, as its only one wheel I worked on.