The use of the article "THE" + position

As a non-English speaker whose native language does not have articles I am always unsure about the use of them. This time I would like to clarify the use of the article "THE" together with positions of persons. For example:

John Smith and the director of my department Adam Gray went to a meeting yesterday.

If I state the name of the person do I need "THE"? I understand that if I said just "John and the director of my department went..." "THE" would be necessary but does that change when stating the name also?

Similarly, do I need to put "THE" in this type of sentence:

The Prime Minister of the United Kingdom David Cameron announced changes in immigration policy.

If I don't need the definite article here then why so? Are the two examples equal?

You can use them with or without an article, but the meaning is ever so slightly different. When you use them without the definite article, THE, then you are using an official title. Grammatically it is like a name, it's a Proper Noun. In this case you need to use capital letters for the title: Managing Director, for example.

When you use the titles or positions without an article, that's just a description of the person's job. Its a bit like saying I'm a teacher. So we can say:

• Managing Director of Leo LT, Kestutis Sliuzas ...

or:

• The managing director of Leo LT, Kestutis Sliuzas ...

The first is a title, the second a description. When we are using the second form we have the option to use capitals if we want to: The Managing Director ...

In the Original Poster's example:

• John Smith and the director of my department Adam Gray went to a meeting yesterday.

We need to use the definite article here. The reason is that the director of my department is a description, not an official title. However if you wanted to use a title you could:

• John Smith and Director of Marketing, Adam Gray, both attended the meeting.

This is similar to how we use proper noun titles like King or common noun descriptions like king.

• The king of my country is an idiot.
• King of Spain, Felipe VI was asked yesterday ...

Hope his is helpful!

It largely depends on how you put it.

The way you have expressed it in the example, including the definite article would be usual, though not essential. You could just about get away with saying:

JS, and Director of my department, Adam Gray, went to a meeting yesterday - but it doesn't sound right.

However if you said:

JS, and Adam Gray, Director of my department, went to a meeting; the article is more easily dropped.

Or you could say:

David Cameron, Prime Minister of the UK, made a speech to the Security Council.

But if you put the title first you really need the article.