\documentclass[a4paper,10pt,twoside]{report}
\usepackage{BEPstyle}
\usepackage{import}
\usepackage{verbatim}
\usepackage{graphics}

\usepackage[final]{pdfpages}
\usepackage{subfiles} %should be last

\addto\captionsbritish{\renewcommand{\contentsname}{Table of Contents}}

\newcommand{\numimagefolder}{./numericalsetup/nsimages/}


\begin{document}

\includepdf[pages=1]{./titlepage/titlepage.pdf}

\chapter{Numerical set-up}\label{chapter:Numerical set-up}
\subfile{numericalsetup/numericalsetup}

\end{document}
\renewcommand{\numimagefolder}{nsimages/}