forget the A1 Luisa!!
I came up to yorkshire from London a few weekends ago on the M1, the BIS (the later watercooled model made from 87'-92') can cruise happily at 65-70mph as apposed to the aircooled models which have a top speed of about 60-65 tops. My 126 BIS did 60 miles to the gallon! However the car does get blown about a bit with the cross winds and lorries passing.
The BIS also has the engine under the floor so to speak so you have the advantage of a boot and a proper hatcback with seats that fold down. Some people say that the BIS isnt as reliable as the older aircooled models, however this is largely down to people not maintaining them properly.
With regard to private sales, its good that you are concerned as there are alot of con men out there. Ebay can be a dodgy place to buy from so make sure you see the car first, before bidding. Prefferably take someone who knows a little about cars, you can make sure you get a receipt that you both sign,
if its a water cooled 126 (BIS) ask if the head gasket has ever been done
I would suggest that you get a car with a new MOT or one which has at least 6 months remaining, as you can then get it taxed (if its not already) and will be a road legal car for you and your dad to use after you have insured it of course.
another thing you could check for is if the Kingpins are worn, xif it has just had a legitimate MOT then they should be fine.
Watch out for rust make sure there are no massive holes, as there will probably be some more rust in the critical MOT failng areas too.
hope all this info helps, just ask away on here any questions you need answering.
regards
Chris