It's an uncommon use of the word 'job', which normally means 'work'. However, occasionally it can be used to refer to an item upon which a job was done in a specific manner. In this case, it's a car that was made in England and has the characteristics of a specifically English-made car; therefore it is an "English job". Think of it as a complex synonym for "specific item".

From Thefreedictionary: Informal - An example of a specified type, especially of something made or constructed. Often used in combination: a new building that is just another glass and steel job; a cowboy hat that is one of those ten-gallon jobs.