Hi,
I would say you would probably be struggling to get a reception of Astra 2D with even a 5 metre prime focus dish, because in the Caneries they need at least a 3 metre dish to get most Horizontal transponders also they do not get many vertical transponders at all with dishes of that size. But you could have a sidelobe in your favour, which will give you a chance of receiving most of the Horizontal transponders, you will not know until you try. I suggest you try with a cheap 2.4 metre dish first and see if you can get a few transponders or not, if you can then move up to a 4.5 or 5 metre dish. Do not try first with a 5 metre dish, because they are very expensive. But if you want Astra B south which carries Channel 4 and many other SKY channels. I would say a 2.4 metre dish should get you many of the sky channels on that satellite. But for Channel 5 which is on Astra b north, you will probably not get.
A much cheaper solution for you would be for you to use a slingbox if you want uk tv. Just ask someone in the uk is it o.k for you to connect it to their aerial system and their internet. Then the box will stream freeview uk tv channels to you anywhere in the world.
Regards Stu