The Tango Serida is one of a number of sequence dances which are popular in the UK and some other countries such as Australia, New Zealand and Canada. These are choreographed dances with a pattern which repeats, usually every 16 bars. 30 to 40 new dances are published each year, each having one a competition for "inventive" dances. Most rhythms and styles are represented with the competitions categorised into three groups, Modern, Latin, and Classical (previously known as Old Time).
With so many new dances appearing most of them quickly fade into obscurity but the Tango Serida is one which has become an established standard. I believe it dates from around 1960. It is a Classical/Old Time tango which differs from a modern ballroom tango in that partners may separate for solo turns and may dance in a side by side or "shadow" position.
Howard