Scrubbing is used where a tyre is being dragged along the ground sideways, rather than rolling along as you would expect. That's an extreme explanation, as it's likely your tyres are only pointing off by a few degrees which is nothing in the real world, but over many miles it can make a big difference to the tyre.
Tracking/alignment/geo should be done annually at least, if not every 6mths if you drive over some really poor roads regularly. In MK though, annually will be just fine.