Client has country specific (.co.uk) but no international domain name

[McTaggart]

Is there any issue re: SEO?

I usually go for a local and international domain just to protect brand but these guys only protected local .co.uk domain. I'm thinking there aren't any specific SEO implications, but please let me know if there are any...

[Stramark]

if customers start looking for the .com domainname (direct traffic) you will loose some customers.

Especially if the .com does exist and offers similar products/services.

[ZephSnapp]

You should always protect the brand.  But the question is, are their any SEO implications for the work that you are going to do?  
The answer is not much.  If you do an awesome job on you client site, you should be fine.