laches or whatever it's called in the UK.
From a cached page on the Brennan website (URL now returns a 404)
In 2006 the British Phonographic Institute or BPI said to a parliamentary select committee that they wanted to “make it unequivocally clear to the consumer that if they copy their CDs for their own private use in order to move the music from format to format we will not pursue them"
So the effect of the passage of time on enforcement of rights will be of interest.
There's a helpful discussion here