I have had a .com domain for a number of years. As a web design
company, I have used the '.com' as part of my branding. I have and
continue to serve an international market.

However, I am based in the UK, which has now become a critical market
for me, but my site is not listed in the 'Pages from the UK', and
performs worse in google.co.uk than google.com.

So, my question is, how do I add the .co.uk domain to the .com domain,
so as to retain the .com for brand and the international market,
without incurring duplicate content penalties, losing the benefit of
domain age and the links I've won, or dividing my link building and
content management efforts between 2 domains?

Many thanks,
Iain