Not to be too harsh on Brown this is the EU so whether or not he changed his mind isn't particularly relevant, the EU will do as it wishes. Can we really be surprised that an intrinsically protectionist organisation as the EU (built from a Customs Union don't forget) would be in favour of protectionism?
From what I know of Gordon Brown (remember, I am a provincial American), frankly I am surprised to read that he held (even if only briefly) and espoused such a rational perspective on mercantilism.
And I think Chris Strange has it exactly right.
But what is the solution?
If you withdraw from Europe, isn't that the same as the problem?
Getting out of the E.U. (as Chris Stange, following Ropke, rightly says - even at the start a customs union not a free trade area) would not mean putting taxes (or other restrictions) on imports from individuals or companies in Germany or whereever (or having them do it to individuals and companies based here - at least no more than they do now) as WTO rules would still apply.
As would self interest as "they sell us far more than we sell them" - so a "trade war" to "punish Britain" is not likely (we are dealing with countries where associations of companies have far more influence than they do here - for example the German government, unlike a British government, is not going to support a dispute that seriously hurt German exports).
And getting out of the E.U. would free us from the threat of regulations that may destroy "the City" and (by the threats of the British government) the Channel Islands and Isle of Man also.
What getting out of the E.U. would not achieve is to protect us from Mr Brown's own activities.
For example, today yet another 50 billion Pounds was announced (14 billion of it via Northern Rock - a enity that should have been allowed to close down a long time ago).
This is on top of more than a TRILLION Pounds that the government and the "independent" Bank of England have already spent on bank bailouts and other "recession fighting" antics.
This spending has smashed the financial basis of this country.