I always check out where I am planning on going before I leave home - by using Google Earth. You can even zoom down to see the configuration of difficult junctions - taking into account that in Britain, they drive on the left.
BTW, fuel is more expensive on the motorways & at branded fuel stations such as Esso & BP. Try & buy fuel at the big supermarkets such as Tesco, Morrisons, Sainsbury or Asda (Walmart). These supermarkets usually have road atlases at low prices.
Please note that you must not overtake on the inside. So, on a 3 lane motorway, you will normally find slow stuff in the left lane & fast traffic overtaking in the right hand lane. You should not hog any lane. If you were in the middle lane & the left lane is empty - you should move to that lane. People will often drive above the 70mph speed limit on motorways. However, police do set up mobile speed traps & gantries often have speed cameras. Britain is one of the safest places to drive.