Iains, Have you looked at the graph provided by Nigel, who I would consider one of your "allies" in this dsicussion.

During much of the Labour Governments term of office the pound traded at a much higher level. Only occasionally has it reached the same heights under a Conservative/Coalition Government.

You can see the figures for yourself.

However, this is a distraction from the discussion that the Pound has significantly weakened against the Euro since the Brexit vote. That is a fact which is clear to see in the graph kindly provided by Nigel.