If you really want a forced saving experience with tax remove your claim to the tax free threshold for that job. Do that and I can basically guarantee you'll be sitting on a fat return every year.
The downside is of course that getting that tax return means you didn't have that money for the rest of the year, which is good if you can't save otherwise but means you didn't even get the pittance of interest you could have gotten if you had it (not to mention making your life hard if the weekly budget was already tight).