I'd say it was a feature of a certain social dialect. In shops where I live (not West Country), you're quite likely to hear What was you after? However, the OED has an entry for to be after in the sense of 'To be trying to get or achieve (something)' with no usage comment.

I'd have said it was a feature of a certain social dialect. In shops where I live (not West Country), you're quite likely to hear What was you after? However, the OED has an entry for to be after in the sense of 'To be trying to get or achieve (something)' with no usage comment.