Software for apportionment retail scheme

I have a client who uses an ancient version of Simplex software to do the bookkeeping for his Post Office/shop.  He uses the apportionment scheme.

The software is awful to look at and to use and from our point of view, extremely difficult to extract information from when preparing the accounts.  It is also getting to the point where if he upgrades his computer it will become incompatible.  He is already in a situation where he cannot print from it.

He asked if I knew of any software which would be able to cope with the VAT scheme.  I have looked and looked but can't seem to find anything suitable.

Does anyone know of/use any software which could help us?

Many thanks.