It does depend a little on how much and which direction you drift. If you're a right-hander, I would suggest that drifting right is something you want to avoid (it will stop you going very deep on the approach if you need to) other than that, as suggested previously, as long as you're consistent it's ok.
I assume that if you're posting here, that it's not. What I usually do is mark the board I want to finish on at the line with black electrical tape and bowl a few to see how far away I am, then I'll get someone to watch my feet during each step and see where they're going, marking each one with tape. From there I can work out which step is the biggest problem and then move the tape to where I want my foot to be. I'll then run through the approach a few times so I can get used to it. If your drift is really inconsistent, then there may be a balance problem in there that would nee looking at too.
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Reporting from England