Changing predefined words in a biblatex bibliography

Question

My university calls for a Harvard style and Biblatex style authoryear works well. For online sources it requires this

I have managed to change the standard URL: to '[Online]. Available at' with

\usepackage[minbibnames=1,maxbibnames=99,maxcitenames=2,backend=biber,
style=authoryear,firstinits=true,dashed=false,natbib=true,url=true,
bibencoding=utf8,isbn=false]{biblatex}
\addbibresource{refa.bib}% 

\DefineBibliographyStrings{english}{%
urlseen = {Accessed}
}
\DeclareFieldFormat{url}{\bibstring{[Online]. Available at}\space\url{#1}}

But it is rendering as

with text in bold and the first letter lower case, any ideas?

Here is a MWE

\documentclass[11pt,oneside,british]{scrbook}
\usepackage{scrhack}
\usepackage{amsmath}
\usepackage{setspace}
\usepackage[british]{babel}

\usepackage[minbibnames=1,maxbibnames=99,maxcitenames=2,backend=biber,style=authoryear,
firstinits=true,dashed=false,natbib=true,url=true,bibencoding=utf8,isbn=false]{biblatex}
\addbibresource{refa.bib}% 

\DefineBibliographyStrings{english}{%
  urlseen = {Accessed}
}

\DeclareFieldFormat{url}{\bibstring{[Online]. Available at}\space\url{#1}}

\begin{document}

\cite{schmitt_gradient_2013}

\printbibliography[heading=bibintoc]

\end{document}

Answer 1

\documentclass{article}
\usepackage[british]{babel}

\usepackage{biblatex}
\addbibresource{biblatex-examples.bib}% 

\DefineBibliographyStrings{english}{%
    urlseen = {Accessed}
}

\DefineBibliographyStrings{english}{%
    urlseen = {Accessed},
    url = {[Online]. Available at}
}
\DeclareFieldFormat{url}{\bibstring{url}\space\url{#1}}

\begin{document}

\cite{ctan}

\printbibliography

\end{document}