1) I think that the company may be looking out for their own interests.
I say this because you led their list of reasons to proceed with (1) the invention is only made in the UK, and (2) it's not already patented - those are not valid reasons to proceed. The last reason, they can improve the invention (i.e., design around the prior art), is the only valid reason to proceed and seems almost like an afterthought. 35 U.S.C. 102(a) gives conditions for patentability with respect to novelty and the prior art, and you are not entitled to a patent if the claimed invention is described in a printed publication, in public use, on sale, or otherwise already available to the public.
2) If you're unsure whether the UK product is the same as yours, the invention development company should be able to tell you what they think you could claim as your invention, and what the difference is between your claimed invention and the UK product. New inventors frequently do not realize how subtle a difference can be and still distinguish over the prior art. You would have to decide whether this difference is worth pursuing in a patent application.
I doubt the invention development company will do this for free. I wouldn't - it's more work than most people realize.
3) For the invention development company to really tell you whether you should proceed, you should get a prior art search done. The company has no way of knowing whether your idea is patentable without searching the prior art.
Without the prior art search, you're really just hoping that no one else has had your idea already. A full patent application costs much more than the basic prior art search; you have to decide whether do an art search. Since a simple Google search turned up a similar product, I would be reluctant to proceed without any prior art search, but that's your call.
A full patentability analysis is expensive; I doubt you are willing to pay the company to do such a thing. So, what you usually get (for a "knock-out" prior art search costing $500 to $1000) is a survey of the state of the art to give you an idea of what's out there - this will not be a guarantee that your invention doesn't exist already.
Alternatively, you can do a prior art search yourself. First, I would read a book like "Patent It Yourself" by David Pressman, and then do some digging to see what you can find out there.
Any way you do the search, the invention development company will not study the prior art and advise you for free. Even if they contract out the art search (which almost all firms do), reviewing the results is time consuming.
4) Be wary if your invention development company only prepares provisional applications. A provisional patent application is not a patent application and will never become a patent - it automatically dies after a year and it confers no patent rights per se. You will have to file a non-provisional patent application claiming priority to the provisional patent application to actually try to get a patent. I don't trust provisional-patent-only firms - I think many are shady and trying to take advantage of the little guys.
I advise all independent inventors to read books like "Patent It Yourself" by David Pressman in order to orient yourself to the patent process. You can probably get understandable patent books from your local library. It is quite easy to pay a lot of money for a worthless patent; a knowledgeable inventor will get much more value for his or her money.