Reed warned Marketing at the Business Funding Show of the dangers of leaving the EU and its "complete and unfettered access to one set of regulations for 27 countries".
"People moan about the regulation in the EU but it makes it easier to do business," says Reed. "We [Innocent] do business with 16 countries in the EU and one that is out. For the one that is out we have to hand sticker every single bottle with a bit of extra labelling - it is insane."
He concedes there have to be compromises when part of a union comprising 28 nations, but adds the combined power of the EU "makes it the biggest game in town" and a larger market for UK trade than America or China.
"It is a colossal opportunity on our doorstep and we are the gateway to it," says Reed. "The most obvious and simple point that any marketer knows is that when given the choice of being able to sell to 60m people or 500m people you would choose 500m people every time and that is the difference of being in the EU and out of it."
Referendum expected in June
Reed still remains on the board of Innocent following it being sold to Coca-Cola in 2013 in a deal that valued it at £320m.
Alongside his Britain Stronger in Europe role, he also runs Jam Jar investments, a venture capital firm aimed at consumer goods.
Before taking on the Britain Stronger in Europe role, Reed showed his interest in politics by signing an open letter ahead of last May’s general election voicing support for the Liberal Democrats remaining in power.
Britain Stronger in Europe is an advocacy group fighting to persuade the British public to vote to remain in the EU. It is headed by former Marks & Spencer boss Stuart Rose.
Prime minister David Cameron is in the midst of negotiations with EU ahead of an expected referendum in June. Earlier today, the EU published a draft deal that will grant the UK partial concessions if it votes to stay in the EU.