Have now had time to do a bit of research on the topic and a bit shocked to tell the truth at the level of complacency about the use or 'spreadsheets' for complex calculations.
I have started to look into one of codes that I will be looking to convert into a more structured environment and its not pretty. Rather than it actually being a spreadsheet it is in fact a large Visual Basic code! All Excel is being used for is essentially input and output of data. Which in some ways is good because at least there is a chance of understanding the code operation. But on the other hand is bad in that this code has not been 'designed' but, and there is no other way of saying this, hacked out over a period of years. I am now finding that this is a common occurrence!
Why on Earth do people believe this is an appropriate way of developing what has turned out to be a very complex piece of software? It's sort of akin to doing DIY on your house - add a bit here, chop a bit there - but then again for the safety critical jobs eg the electrics you still need a qualified electrician to certify what has been done is OK - not so with hacking out code hidden within an Excel wrapper.
The other issue I have come across is, for some people, if you say a model has been developed in Excel they seem quite happy to accept this without question. It's as if just by using Excel you have proved that what has been done will be OK for use - we all know Excel don't we, come on, can't be that bad - kind of thinking!
Personally, letting people loose on Excel for complex calculations scares the pants off me - and others - check out this link to see the full extent of the damage that can be caused!
BUT wrapping, what is essentially a VB code, up under an Excel umbrella - which as noted above, if you say its an Excel model you can go a long way without having to declare what you are really up to - is a bigger crime. Especially when committed by engineers - who should know better!
Stand down off soap box and CONTINUE ;)