Björn Ulvaeus and Benny Andersson bounded down the narrow staircase.

Agnetha Fältskog and Anni-Frid Lyngstad followed more quietly behind them.

Nobody had ever spotted the four members of ABBA on their regular visits to Northumberland. It was our family secret that they always spent their holidays with my sister and her husband at their cottage on the Holy Island of Lindisfarne.