Was looking to do something similar and you may have realised this by now but if you were looking to strip out the VAT element of what were originally gross prices, using 17.5% reduction will leave you with an incorrect net price. VAT is calculated as a % of the net (exclusive) price what you are doing is reducing the price by 17.5% of the gross (inclusive).
For example 100 x 1.175 is 117.5 (you have added 17.5% to 100) but 117.5 x 0.825 will not get you back to 100...
What you need to do is reduce the gross prices by 7/47ths of the gross which would give you the correct net price.




