I don't believe the removal of the gold standard was the primary reason for the UK's decline. The gold standard was removed because it was becoming unworkable, why wouldn't the same problems exist now?
From wikipedia regarding the floating of the pound: With the break down of the Bretton Woods system — not least because mainly British currency dealers had created a substantial Eurodollar market which made the U.S. dollar's gold standard harder for its government to maintain — the pound was floated in the early 1970s and so became subject to a market appreciation. The Sterling Area effectively ended at this time when the majority of its members also chose to float freely against the pound and the dollar.
