Bit of an unusual request here.  Does anyone know of a tool or bit of code that will extract a list of 1km squares from a DINTY tetrad grid reference i.e. NT24A would produce NT2040, NT2140, NT2041, NT2141?  Preferably something written in Excel or Access so that I could plug a list of grid references in and get it to convert them all at once, but anything would do at the moment.