They wanted to get in to get on. The getting on part worked for a while but it doesn't seem to anymore and to keep it working they've got to get out. So the "we've got to get in to get on" in 1972 changed to "we've got to get out to get on" by 2016.
The UK joined the EU in 1973 together with Denmark. The two countries remained probably the most sceptical members of the Union and both did not joined the Euro, the UK kept the pound and Denmark the krone.