Fitting lez compliant filters

Hiya all. I am completely new to the club. We were just about to get going with our newly purchased Campervan, when we came across the dreaded LEZ compliance requirement. We live in London, and had not planned for this! Does anyone know of a supplier and fitter of LEZ compliant filters for exhaust systems, that they can reccommend? We have a Ford Transit ( REIMO conversion) 1997 with 2.5 ltr engine Diesel.

    Thanks