Will it damage the gearbox and if so why? Surly if the gearbox in neutral it will be ok
Consult the handbook. Generally the gearbox internal oil pump is driven off the input side so when towing on the drive wheels without engine running parts of box are spinning without being fed oil.
Can you put the car into neutral without the engine running?
I’ve got an auto and you can only move out of ‘park’ if the engine’s running and you’ve got your foot on the brake.
Generally speaking only for a limited distance and at a reduced speed, maybe 30-50 miles at perhaps 50mph. Towing in neutral should be ok within these kind of limits but you should check your manual for precise information.
Not bought the car yet, but it would seem that if I buy an old auto jag and left it running whilst being towed that would work right?
Better off disconnecting the prop shaft.
Or lifting the driving wheels if you can. It does depend on the auto. Some really ancient stuff (and I’m talking early 60s here) can sometime be towed (and even tow-started) as their pumps run off the output side.
It would drink a load of juice if you left it running. What’s stopping it moving under it’s owner power?
But do you think it will do fatal damage if I don’t, need it to be handy to tow on a frame behind my bus
Just disconnect the prop or suspend tow or trailer.
Trailers and suspend tows are to bulky and nowhere to store. I live on a double decker and tow my old A class behind. Thing is its knacked and I’m looking for a grand’s worth of motor. Would like an old Jag but from time to time I move round on bus and need to tow car, but no point getting auto if its going to knack it but would prefer an auto.
Anyway, towing autos aside…
Towing anything more than the tiniest microcar isn’t an option on a pole. 
In the USA where evrything is automatic they tow cars and 4x4s behind their camper vans, they go for hundreds and hundreds of miles at normal speeds, I always thought that you couldn’t tow an automatic, so you must be able too, I can’t see the geriatric old gits disconnecting driveshafts or anything and yank cars are not very technologically advanced 
It does Fatal Damage if the Oil Pump is powered by input,but,in USA they tow your Car all way along behind there Mobile Homes and it does no damage.
Check with the Manuell,The Car dealer,AA,RAC,or Mobile Home-Tow Specialist.
Read 
traveltips.usatoday.com/tow-car- … 21075.html
ehow.com/how_2123302_tow-car-behind-rv.html
ukcampsite.co.uk/articles/view.asp?id=18
If you could exchange your Car?
against a B-Cycle?
watch the Pics of car Transport.
Get you a small Trailer
viewtopic.php?f=2&t=37818&start=210
marlow:
Not bought the car yet, but it would seem that if I buy an old auto jag and left it running whilst being towed that would work right?
How old a Jag is it ? If it’s the old BW box, you’re supposed to either drop the prop shaft, lift the drive wheels, or overfill it with oil. The cars that could be towed with no problems were things like Vauxhalls with a Hydramatic box. They had a front and rear pump, so that if the engine was running or just the wheels were being turned by towing, you still had oil circulating in the gearbox.
Why nor have a look for a shed with a manual box.
To be honest, to be on the safe side, I’d drop the prop shaft, it’s not like it’s a hard job, can even just drop 1 side and strap it up if you can’t be arsed taking it fully off everytime.
Towing a RWD rigid axle auto I used to take out one half shaft…
newmercman:
In the USA where evrything is automatic they tow cars and 4x4s behind their camper vans, they go for hundreds and hundreds of miles at normal speeds, I always thought that you couldn’t tow an automatic, so you must be able too, I can’t see the geriatric old gits disconnecting driveshafts or anything and yank cars are not very technologically advanced
In the states there are allot of kits avalible to make autos towable, these are things like electrically driven oil pumps for the transmission, dissengagable rear diffs, or quick disconnects for the prop shaft.
There are also wiring kits avalible to contol the cars lights from the towing vehicle with out buggering up the electrics and also linkages for brakes
some also use a frame type devices with wheels that lift the main drive wheels off the ground