With the new CIS Domestic Reverse Charge meaning that a lot of subcontractors are now receiving VAT refunds rather than making quarterly payments, there is the risk that the Direct Debit mandate with HMRC will be cancelled by the user's bank if it is not used for 24m...if the user is then due to make a VAT payment one quarter, the HMRC system will still say it has a direct debit in place, but when they request it, the bank will refuse to honor it and the VAT return is not paid automatically.
Hence is it possible to put a warning pop-up (not sure there is much else you can do!) if a VAT return is generated that has a liability to HMRC following 24 months of refunds. I know you cannot check if the Direct Debit mandate is still valid, but another client of mine has just had this situation and I was wondering if it was possible to try to highlight this potential problem for others so that they can check before it causes them issues with HMRC. Might get you some brownie points for highlighting it!!