After a potential issue was raised regarding my buggy I decided to consult the IVA manual. I'm still looking through it (only just started, it's big..305 pages!) but for anyone else who wants to do some research, here's a link to the section with manuals in:

https://www.gov.uk/vehicle-approval/individual-vehicle-approval-manuals

And here's the link specific for most buggies:

http://www.dft.gov.uk/vosa/repository/M1%20IVA%20Inspection%20Manual.pdf

the second buggy link is the full 305 pages, an awful lot of reading.
From my research if your pan is standard completely standard you can get on the road without an IVA other mods are down to the mot tester to advise of if he wants to or knows of them.
we have an air ride passat at work where the chassis has been notched to clear the drive shafts when sat down that officially requires an IVA but if the mot tester does not spot it and flag it up who will ever notice.
build a buggy for the IVA and it will pass try and trying get an old buggy through without a full rework and you will fail.