http://www.eastsidebiker.de/
– so it *is* a real bike shop, rather than someone set up to look like a bikeshop.
Normally warranties are handled by the local distributor, so if there were any issues you'd probably have to ship it back to Germany.
Interestingly – from the Nicolai-uk website :
http://www.nicolai-uk.com/index.php/warranty-and-faq/nicolai-warranty-five-years/
– the (UK)warranty transfers with the frame – most frame warranties only apply to the original purchaser.
In the English warranty on the manufacturer's site
http://www.nicolai.net/download/pdf/garantie-englisch-17082006.pdf
it also say that you can use your local dealer *OR* ship directly to Nicolai Germany (at your own expense) – so it sounds like you'd be covered both through the German bike shop or by dealing directly with the manufacturer (which is a little unusual)
You *might* be able to get Nicolai-UK to handle it, but since they're almost certainly not part of Nicolai, and wouldn't have made any money on it, you couldn't expect them to.
As Andy said – try asking Nicolai Germany, including about whether you could use the UK distributor too.