MNRebecca wrote:

1.  What makes people common law spouses in the UK?  Living together for an extended amount of time? 
Yes

2.  Why weren't Benedict and Olivia considered common law spouses?  Or were they?
Yes, officially, they would have been considered common law spouses.

3.  Can common law spouses just separate at will, without having to go through any financial or legal hurdles?
Depends, once there are kids separations tend to be more complicated. The whol eidea is that common law partnerships are recognised as similar to full marriage, and thus spouses have rights etc.

4.  Is the phrase "common law" derogatory, antiquated, or resented?  Would Martin or Amanda ever refer to him- or herself as being part of a common law marriage?

Again, that depends. It is probably quite unusual to use the term. However, if you consider adoption, you would mention it. In a circle of friends, or people one doesn't know too well, I only know one couple using this term...

 

The term a common-law husband/wife is really not used much nowadays. It might be used more by people of say, my parent's generation. Until the 1970s the term did have negative connotations but this is not really the case today. Unlikely anyone like Martin and Amanda would use such a term as it is rather outmoded. They would probably refer to each other as 'partner' or possibly husband/wife.

There is a difference in law between Scotland and the rest of the UK. There is a good explanation of what it means in the UK in general and Scotland in Wikipedia. As you will see there is, in fact, no such thing as being a common law spouse in the UK. Separations do not require anything like a divorce but of course partners can claim rights to children and to property etc. These rights are not the same, however, as those of married couples (or those in recognised Civil Partnerships).

Benedict and Olivia may possibly have been regarded as being a couple but 'common-law' would not have been mentioned.

On the Wikipedia link I would just scroll down to the relevant part for UK and maybe Scotland, if you are interested.

http://www.wikipedia.org/wiki/Common-law_marriage