And sorry for the delay (computer crashed)
The US Patent and Trademark Office (link below)http://www.uspto.gov/patents/process/search/
Can allow you to search...though I caution that the web search is not real great...most folks who want to perform a search will pay an attorney to perform the search. This is a more efficient way to search.
If the product is patented or has applied?
I would not sell it in the US as your own product. That opens you up to liability for a violation of US Patent law.
Now...say it is patented in UK only and they have not applied for US patent. Can you sell it here? Can you patent it yourself?
You still run a risk
First, it is unlikely you can patent it...if it is patented in the UK, you are not going to be able to rename it and patent it...the patent process is designed to protect folks who invent products. So your patent application
would not likely be successful.
Can you rename it and sell it?
You could...but you are still running a risk. If they have patented this formula and it is registered in UK only, then technically they can only enforce the patent in UK. But if it is registered in UK then it is a fairly straightforward process to register in the US. So if you launched a sales campaign for this product and then they find out and file to patent in the US, you may find yourself unable to sell it going forward.
Consider a license.
You can negotiate a license with them to brand/market this product. You pay them a fee (whatever you negotiate) and that gives you the rights (for the period you negotiate) to sell this product as your own int he US. If they have no presence? That may be a good way to go about this. But get a lawyer...you want to negotiate this so that if it takes off? Your marketing efforts are successful? That you are protected to be able to sell this for the foreseeable future...you need that language in any contract you negotiate.