\documentclass{article}
\usepackage{web}
\margins{0pt}{0pt}{0pt}{0pt}   %% Kein Seitenrand
\screensize{300mm}{600mm}      %% Dimensionen: H\"{o}he, Breite des Dokuments

\parindent0pt

\usepackage{pstricks,pstricks-add}

\definecolor{ukRed}{RGB}{204 0 0} 
\definecolor{ukBlue}{RGB}{0 0 102}

\begin{document}

\thispagestyle{empty}

\begin{pspicture*}(0,0)(60,30)
%% Flagge (Verh\"{a}ltnis 2 Breite : 1 H\"{o}he)

\def\diag{%
\psframe[linecolor=white,fillstyle=solid,fillcolor=white](-10,0)(70,6)
\psframe[linecolor=ukRed,fillstyle=solid,fillcolor=ukRed](-10,1)(30,3)
\psframe[linecolor=ukRed,fillstyle=solid,fillcolor=ukRed](30,3)(70,5)
}



\psframe[linecolor=ukBlue,fillstyle=solid,fillcolor=ukBlue](0,0)(60,30)
\rput{26.56}(0,-3.3){\diag}
\rput{-26.56}(!0 30 3.3 sub){\diag}

\pspolygon[linecolor=white,fillstyle=solid,fillcolor=white](0,10)(25,10)(25,0)(35,0)(35,10)(60,10)(60,20)(35,20)(35,30)(25,30)(25,20)(0,20)
\pspolygon[linecolor=ukRed,fillstyle=solid,fillcolor=ukRed](0,12)(27,12)(27,0)(33,0)(33,12)(60,12)(60,18)(33,18)(33,30)(27,30)(27,18)(0,18)
\end{pspicture*}
\end{document}
