I think hes giving GB a pat on the back for not taking us into the Euro-zone. in truth it was more likely that the thought of a promised referendum would result in all his aspirations on the matter would founder
The euro may, (or may not), have been a bad thing for the UK. However when the euro was introduced in Jan 2002 the exchange rate for the £ was about €1.50.
At this time it is about 1.13€, which is typical. So much of our imports come from EU countries, thus will have become more expensive with the decline in the £ exchange rate. (Oil is an exception of course, being priced in US$).
The basic problem seems to be the admission into euro zone of certain countries with questionable fiscal policies. This has resulted in a great burden being placed on the rest.
Brussels attitude seemed to have been "the more the merrier", as this has continued to have been their stance in recent years with the admittance of new countries into the EU.