How far are we going back here ?
You can potentially amend your returns to where they should have been, if your income needs reducing to compensate for allocations to spouse.
Probably best to quantify the adjustments by tax year , let the tax officer know that there will be similar adjustments to your returns and perhaps pose the question if anything tax neutral can be left as it is?
I would say it is important here that you should review what has been submitted for you, if you have made any errors on your returns ignoring the wife/you splits then it is highly likely this will be picked up on, so if there are other issues probably best to highlight anything there may be in that regard - rather than let hmrc "uncover them"
Probably best to at a minimum get a review of your calcs if you have any doubts as to how and what should have been claimed and when.
So is it considered worth going direct to hmrc or to an accountant?
You may get away with a compromise solution if you are lucky perhaps a quick chat with the tax inspector explaining where you are will give you an initial indication of how they would like to proceed. I would be surprised if they don't immediately ask for full correct calculations split as they should have been compared to how they were split with relevant computations of how tis would pan out tax wise with all adjustments in place. Basically until you do the full tax calcs you don't really know what the tax consequence is.