LEZ - sorry RLWP I never thought to mention….what model and year is your van? Basically, if you are smaller than a Transit, there is nothing to worry about, if you are Transit sized or bigger then I hope it is post 2002 (Euro 3 compliant). Some pre 2002 vans are as well but check. If you came in a car, you are safe. If you are non-compliant, I think that the first time, you get a stern letter but then the fines are astronomical (the "fee" is £100/day for non-compliant vehicles.)
Worth knowing is that the regs will change from 2015 to being Euro 4 compliant, this means a post 2008/2009 vehicle, a cynic would think that they were trying to put small businesses out of business!