The standard original tyres sizes for a Series 1 discovery are:
205/80R16 = 734.4mm diameter or
235/70R16 = 735.4mm diameter.
The load index also needs to be at least 101 so each tyre can handle 825kg minimum. The speed rating should be "S" minimum so it can take up to 180km/h.
Other tyres sizes:
245/70R16 = 749.4mm diameter
245/75R16 = 773.9mm diameter
245/70R16 fit straight on and depending on the type of tread shouldn't rub on the guards.
245/75R16 also fit straight on, but I'm told you will probably have to trim the rear guard at the bottom slightly.
There is no doubt the tyre dealer you initial saw was a fool! I currently run 235/70R16 on alloys - absolutley 100% legal and no problems at all!
I'm stepping up to 245/75R16's so will see how that goes.

