100% Don't know what the policies were exactly in 1997, but I could only assume you would need either:-
1. Current Driver's Licence issued by your resident country + International Drivers Permit (which as far as I am aware, you can only apply for and get in your home country)
or 2. If in 1997 an IDP was not required (I think there is/was an agreement in place between UK & Aus where you don't need an IDP for the first 12 months of arriving in UK), then I can only assume you would need to pair that with your passport.
I know currently to hire a car in UK/Europe I would need to present my current licence and a passport and in many EU countries an IDP aswell.
And then the rules, of course, are different again if you hold a European drivers licence.